Method and apparatus for performing repetitive transmission of information in time division duplex based cell in wireless communication system

ABSTRACT

Methods and apparatuses are provided in a wireless communication system in which DCI is received from a base station and includes a subband indicator indicating a subband among at least one subband configured for the terminal as an active subband and information indicating at least one frequency resource allocated for a PDSCH within the active subband. The active subband is identified based on the subband indicator. The PDSCH is received from the base station in the active subband based on the information. A size of the DCI is configured based on a size of the active subband.

PRIORITY

This application is a Continuation Application of U.S. application Ser.No. 15/542,609, filed in the U.S. Patent and Trademark Office (USPTO) onJul. 10, 2017, which is a U.S. National Phase Entry of InternationalApplication No. PCT/KR2016/000188, filed on Jan. 8, 2016, which claimspriority to U.S. Provisional Application Nos. 62/101,632, 62/139,347,62/145,207, 62/161,398, 62/174,886, 62/196,585, 62/204,694, and62/240,270, which were filed in the USPTO on Jan. 9, 2015, Mar. 27,2015, Apr. 9, 2015, May 14, 2015, Jun. 12, 2015, Jul. 24, 2015, Aug. 13,2015, and Oct. 12, 2015, respectively, the contents of all of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to cellular wireless communicationsystems, and more specifically, to schemes for communicating controlchannels by low-cost terminals. Further, the present disclosure relatesto schemes for transmitting channel information on serving cells to basestations in wireless communication systems having multiple cells.Further, the present disclosure relates to scheduling schemes for datacommunication by lower-cost terminals.

DISCUSSION OF RELATED ART

To meet the demand for wireless data traffic having increased sincedeployment of 4G (4^(th)-Generation) communication systems, efforts havebeen made to develop an improved 5G (5^(th)-Generation) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), Full. Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

Generally, mobile communication systems have been developed to guaranteeuser activity while providing voice services. Mobile communicationsystems have been expanding service areas from voice to data, and thesystems have been grown to provide high-speed data services. However,more evolved mobile communication systems are required to live up tousers' desire for higher-speed services and lacking resources that arefaced by the current mobile communication systems.

Mobile communication system advances to broadband wireless communicationsystem to provide high data rate and high-quality packet data services,such as 3rd generation partnership (3GPP) high speed packet access(HSPA), long term evolution (LTE), or evolved universal terrestrialradio access (E-UTRA), 3GPP2 high rate packet data (HRPD), ultra mobilebroadband (UMB), and institute of electrical and electronics engineers(IEEE) 802.16e communication standards.

The 3GPP LTE is now underway for standardization as a next-generationcommunication system. LTE is the technology implementing high-speedpacket-based communication with a transmission speed up to 100 Mbps. Tothat end, various approaches are being discussed, and some examplesinclude simplifying the network architecture to reduce the number ofnodes over a communication path and making radio protocols as close toradio channel as possible.

LTE system adopts orthogonal frequency division multiplexing (OFDM) fordownlink and single carrier frequency division multiple access (SC-FDMA)for uplink. Such multiple access scheme allocates and operatestime-frequency resources carrying data or control information per usernot to overlap, i.e., to maintain orthogonality, to therebydifferentiate each user's data or control information. The orthogonalfrequency division multiple access (OFDM) transmission scheme transmitsdata via multiple carriers, and this is a sort of multi-carriermodulation scheme that parallelizes symbols inputted in series andmodulates the same into multiple multi-carriers, i.e., multiplesubcarrier channels with mutual orthogonality and transmits the same.

The LTE system adopts HARQ (Hybrid Automatic Repeat request) scheme thatre-transmits corresponding data through the physical layer in casedecoding fails at the initial stage of transmission. By the HARQ scheme,if the receiver fails to precisely decode data, the receiver transmitsinformation indicating the decoding failure (NACK; NegativeAcknowledgement) to the transmitter so that the transmitter mayre-transmit the corresponding data through the physical layer. Thereceiver raises the data reception capability by combining the datare-transmitted by the transmitter with the data for which decoding hasfailed. Further, in case the receiver precisely decode data, thereceiver may transmit information indicating decoding succeeds (ACK;Acknowledgement) to the transmitter so that the transmitter may transmitnew data.

FIG. 1 is a view illustrating a basic structure of time-frequency domainwhich is radio resource domain where the data or control channel istransmitted on downlink in the LTE system.

In FIG. 1, the horizontal axis refers to the time domain, and thevertical axis refers to the frequency domain. In the time domain, theminimum transmission unit is an OFDM symbol, and N_(symb) 102 OFDMsymbols come together to configure one slot 106, and two slots cometogether to configure one subframe 105. The slot is 0.5 ms long, and thesubframe is 1.0 ms long. One radio frame 114 is a time domain unitconsisting of ten subframes. In the frequency domain, the minimumtransmission unit is subcarrier, and the bandwidth of the overall systemtransmission band consists of a total of NBW (104) subcarriers.

In the OFDM scheme, a modulated signal is positioned in a 2-dimensionalresource constituted of time and frequency. The resources on the timeaxis are differentiated by different OFDM symbols and they areorthogonal to each other. The resources on the frequency axis aredifferentiated by different subcarriers and they are also orthogonal toeach other. That is, in the OFDM scheme, one minimum unit resource maybe indicated by designating a particular OFDM symbol on the time axisand a particular subcarrier on the frequency axis, and this is called aresource element (RE) 112. Since different REs maintain theorthogonality even when undergoing frequency selective channel, signalstransmitted via different REs may be received on the reception sidewithout mutual interference.

The physical channel is a channel of a physical layer transmitting amodulated symbol obtained by modulating one or more coded bit streams.The orthogonal frequency division multiple access (OFDMA) system mayconfigure and transmit a plurality of physical channels depending on thereceiver or the purpose of information streams transmitted. The RE whereone physical channel should be disposed and transmitted should bepreviously agreed between the transmitter and the receiver, and suchrule is referred to as mapping.

In the time-frequency domain, the basic unit of resources is RE 112, andthis may be represented with OFDM symbol indexes and subframe indexes.Resource block (RB) 108 or physical resource block (PRB) is defined withN_(symb) (102) continuous OFDM symbols in the time domain and N_(RB)(110) continuous subcarriers in the frequency domain. Accordingly, oneRB 108 includes Nsymb×NRB REs (112). Generally, the minimum transmissionunit of data is RB. Generally, in the LTE system, Nsymb=7, NRB=12, and,NBW and NRB are proportional to the bandwidth of system transmissionband. The data rate increases in proportion to the number of RBsscheduled for terminal. The LTE system defines and operates sixtransmission bandwidths. For the frequency division duplex (FDD) systemdifferentiating and operating downlink and uplink with frequencies,downlink transmission bandwidth may differ from uplink transmissionbandwidth. The channel bandwidth refers to a radio frequency (RF)bandwidth corresponding to the system transmission bandwidth.

Table 1 represents the correlation between system transmission bandwidthand channel bandwidth defined in the LTE system. For example, the LTEsystem having a 10 MHz channel bandwidth has a transmission bandwidthconsisting of 50 RBs.

TABLE 1 Channel bandwidth BW_(Channel) [MHz] 1.4 3 5 10 15 20Transmission bandwidth 6 15 25 50 75 100 configuration N_(RB)

Downlink control information is transmitted within first N OFDM symbolsin the subframe. Generally, N={1, 2, 3}. Accordingly, N is varieddepending on the amount of control information to be transmitted in thecurrent subframe. The control information may include a control channeltransmission period indicator indicating how many OFDM symbols thecontrol information is transmitted over, scheduling information ondownlink data or uplink data, and HARQ ACK/NACK signal.

In the LTE system, the scheduling information on downlink data or uplinkdata is transferred through downlink control information (DCI) from thebase station to the terminal. Uplink (UL) means radio link through whichthe terminal transmits data or control signal to the base station, anddownlink (DL) means radio link through which the base station transmitsdata or control signal to the terminal. DCI defines various formats, anda defined DCI format applies and operates depending on whetherscheduling information (i.e., UL grant) for uplink data or schedulinginformation (i.e., DL grant) for downlink data, whether controlinformation is small-sized compact DCI, whether spatial multiplexingapplies using multiple antennas, and whether DCI for power control ornot. For example, DCI format 1 that is scheduling control information(DL grant) for downlink data may be configured to include at least thefollowing control information.

Resource allocation type 0/1 flag): notifies whether resource allocationtype is type 0 or type 1. Type 0 allocates resources in RBG (resourceblock group) units by applying bitmap scheme. In the LTE system, thebasic unit of scheduling is RB (resource block) represented in time andfrequency domain resources, and RBG consists of a plurality of RBs andbecomes the basic unit of scheduling in the type 0 scheme. Type 1 allowsfor allocation of a particular RB in the RBG.

Resource block assignment: notifies RB allocated for data transmission.resource represented according to system bandwidth and resourceallocation scheme is determined.

Modulation and coding scheme (MCS: notifies the size of transport blockthat is data to be transmitted and modulation scheme used for datatransmission.

HARQ process number: notifies process number of HARQ.

New data indicator: notifies whether HARQ initial transmission orre-transmission.

Redundancy version: notifies redundancy version of HARQ.

TPC (Transmit Power Control) command for PUCCH (Physical Uplink ControlCHannel): notifies transmit power control command for uplink controlchannel PUCCH.

The DCI undergoes channel coding and modulation and is transmittedthrough downlink physical control channel PDCCH (Physical downlinkcontrol channel) or EPDCCH (Enhanced PDCCH). The PDCCH region that is acontrol channel region and the ePDCCH region transmitted in the datachannel region are split in the time domain and transmitted. This is forquickly receiving and demodulating control channel signals.

Generally, the DCI is subject to channel coding independently for eachterminal and is then configured of independent PDCCH and transmitted.PDCCH in the time domain is mapped and transmitted during controlchannel transmission period. The position of mapping of PDCCH in thefrequency domain is determined by the identifier (ID) of each terminaland spread over the overall system transmission band. That is, in suchform, one control channel is split into smaller units of controlchannels that are then distributed over the overall downlinktransmission band.

The downlink data is transmitted through physical channel for downlinkdata transmission, PDSCH (physical downlink shared channel). PDSCH istransmitted after the control channel transmission period, and thespecific mapping position in the frequency domain, modulation scheme, orother scheduling information are notified by the DCI transmitted throughthe PDCCH.

Through the MCS consisting of five bits among the control informationconstituting the DCI, the base station notifies the terminal of themodulation scheme that has applied to the PDSCH to be transmitted andthe size of data to be transmitted, i.e., transport block size (TBS).The TBS corresponds to the size before applying channel coding for errorcorrection to the data (i.e., transport block (TB)) to be transmitted bythe base station.

Physical uplink channels are generally divided into control channels(PUCCH) and data channels (PUSCH). When there is no data channel, aresponse channel to the downlink data channel and other feedbackinformation may be transmitted through the control channel, and when thedata channel is present, such channel and data may be transmittedthrough the data channel.

The LTE system supports the following modulation schemes: quadraturephase shift keying (QPSK), 16 quadrature amplitude modulation (16QAM),64QAM, and their respective modulation orders (i.e., Qm) are 2, 4, and6. That is, QPSK may transmit two bits per symbol, 16QAM four bits persymbol, and 64QAM six bits per symbol.

Generally, time division duplex (TDD) communication system uses commonfrequency for downlink and uplink and operate distinctively betweencommunication of uplink signals and communication of downlink signals inthe time domain. LTE TDD transmits uplink signals and downlink signalswith the signals differentiated per subframe. Depending on uplink anddownlink traffic load, uplink/downlink subframes may be evenly separatedor more subframes may be assigned for downlink than uplink or moresubframes may be assigned for uplink than downlink.

TABLE 2 Uplink-downlink Subframe number configuration 0 1 2 3 4 5 6 7 89 0 D S U U U D S U U U 1 D S U U D D S U U D 2 D S U D D D S U D D 3 DS U U U D D D D D 4 D S U U D D D D D D 5 D S U D D D D D D D 6 D S U UU D S U U D

Table 2 shows TDD uplink-downlink configuration defined in LTE. In Table2, D denotes subframe configured for downlink transmission, U denotessubframe configured for uplink transmission, and S denotes specialsubframe consisting of downlink pilot time slot (DwPTS) and guard period(GP), uplink pilot time slot (UpPTS). In DwPTS, like normal subframe,control information may be transmitted on downlink, and in case DwPTS islong enough depending on the configuration of the special subframe,downlink data transmission is also possible. GP is an interval to taketransmission shift from downlink to uplink and its length is determineddepending on network settings. UpPTS is used for random access channel(RACH) transmission for random access or sounding reference signal (SRS)transmission of terminal necessary to estimate uplink channel status.

For example, in case of TDD UL-DL configuration #6, downlink data andcontrol information may be transmitted in subframes #0, #5, and #9, anduplink data and control information may be transmitted in subframes #2,#3, #4, #7, and #8. In subframes #1 and #6 corresponding to the specialsubframe, downlink control information, and in some cases, downlinkdata, may be transmitted, and SRS or RACH transmission is possible onuplink.

In TDD system, downlink or uplink signal transmission is permitted onlyfor a particular time period, and thus, specific timing relationsbetween uplink/downlink physical channels mutually related, such ascontrol channel for data scheduling, data channel scheduled, and HARQACK/NACK channel corresponding to data channel need to be defined.

Further, 3GPP LTE Rel-10 adopted bandwidth expanding technology tosupport more data traffic than LTE rel-8. The above technology which iscalled bandwidth extension or Carrier Aggregation (CA) may extend bandto increase the volume of data transmitted as much as the band extendedas compared with LTE rel-8 terminal transmitting data within a singleband. Each of the bands is called component carrier (CC), and LTE rel-8terminal has been specified to have one component carrier for each ofdownlink and uplink. Further, downlink component carrier and uplinkcomponent carrier connected thereto via system information block (SIB)-2are collectively called cell. The SIB-2 connection between the downlinkcomponent carrier and the uplink component carrier is transmittedthrough a terminal-dedicated signal. CA-supporting terminal may receivedownlink data through multiple serving cells and transmit uplink data.

In Rel-10, when the base station has difficulty sending PDCCH (physicaldownlink control channel) in a particular serving cell to a particularterminal, a carrier indicator field (CIF) may be configured as a fieldto indicate that PDCCH is transmitted through other serving cell and thecorresponding PDCCH indicates the PDSCH (physical downlink sharedchannel) or PUSCH (physical uplink shared channel) of other servingcell. The CIF may be configured in CA-supporting terminal. The CIF hasbeen defined to be able to indicate other serving cell by adding threebits to the PDCCH information in the particular serving cell, and theCIF is included only upon cross carrier scheduling, and in case CIF isnot included, cross-carrier scheduling is not performed. When CIF ispresent in downlink allocation information (DL assignment), the CIFindicates the serving cell where the PDSCH scheduled by DL assignment isto be transmitted, and when the CIF is present in uplink resourceallocation information (UL grant), the CIF indicates the serving cellwhere the PUSCH scheduled by the UL grant is to be transmitted.

As such, LTE-10 defines the CA, enabling multiple serving cells to beconfigured for a terminal. The terminal periodically or aperiodicallytransmits channel information on multiple serving cells to the basestation in order for data scheduling on the base station.

Meanwhile, the concept of expanding the number of serving cells up to 32using unlicensed bands for LTE-13 is now in discussion. In such case,transmissions of channel information on multiple serving cells in onesubframe may conflict with each other. Accordingly, highlighted is aneed for a method for supporting an operation of the terminal that mayperiodically transmit channel information on as many serving cells aspossible in one subframe.

Further, for low-cost terminals having the maximum bandwidth limited toless than 20 MHz (e.g., 1.4 MHz), there is a need for communicationoperations differentiated from those of typical legacy LTE terminalsbecause the low-cost terminals support only some subband in the wholechannel bandwidth.

SUMMARY

According to the present disclosure, there are provided a controlchannel transmission method and apparatus for low-cost terminalssupporting repetitive transmission to enhance coverage.

According to the present disclosure, there are provided a method andapparatus for transmitting channel information on multiple serving cellsby a terminal without wasting transmission resources of downlink controlchannels in a wireless communication system supportive of carrieraggregation. According to the present disclosure, there are provided amethod and apparatus for increasing transmission by performingscheduling optimized for serving cells by receiving channel informationperiodically transmitted from a terminal.

According to the present disclosure, there are provided schemes fortransmitting channel information on multiple serving cells by a terminalwithout wasting transmission resources of downlink control channels in awireless communication system supportive of carrier aggregation.

There are proposed a method for configuring periodic channel informationtransmission for multiple serving cells without wasting PDCCHtransmission resources by the base station under the CA situation and amethod for transmitting channel information for the serving cells.

According to the present disclosure, described is a method forconfiguring UCI PUSCH (uplink control information PUSCH) transmissionfor allowing the terminal to perform periodic channel informationtransmission operation on multiple serving cells without the basestation wasting PDCCH transmission resources.

According to the present disclosure, there are provided schedulingmethods and communication methods for operating both normal LTE terminaland low-cost terminal in the same system.

According to the present disclosure, a method performed by a terminal ina wireless communication system is provided. DCI is received from a basestation and includes a subband indicator indicating a subband among atleast one subband configured for the terminal as an active subband andinformation indicating at least one frequency resource allocated for aPDSCH within the active subband. The active subband is identified basedon the subband indicator. The PDSCH is received from the base station inthe active subband based on the information. A size of the DCI isconfigured based on a size of the active subband.

According to the present disclosure, a method performed by a basestation in a wireless communication system is provided. DCI isconfigured including a subband indicator indicating a subband among atleast one subband configured for a terminal as an active subband andinformation indicating at least one frequency resource allocated forPDSCH within the active subband. The configured DCI is transmitted tothe terminal. The PDSCH is transmitted to the terminal in the activesubband based on the information. A size of the DCI is configured basedon a size of the active subband.

According to the present disclosure, a terminal is provided in awireless communication system. The terminal includes a transceiver andat least one processor. The at least one processor is configured toreceive, from a base station, DCI including a subband indicatorindicating a subband among at least one subband configured for theterminal as an active subband and information indicating at least onefrequency resource allocated for PDSCH within the active subband. The atleast one processor is also configured to identify the active subbandbased on the subband indicator, and receive, from the base station, thePDSCH in the active subband based on the information. A size of the DCIis configured based on a size of the active subband.

According to the present disclosure, a base station is provided in awireless communication system. The base station includes a transceiverand at least one processor. The at least one processor is configured toconfigure DCI including a subband indicator indicating a subband amongat least one subband configured for a terminal as an active subband andinformation indicating at least one frequency resource allocated for aPDSCH within the active subband. The at least one processor is alsoconfigured to transmit, to the terminal, the configured DCI, andtransmit, to the terminal, the PDSCH in the active subband based on theinformation. A size of the DCI is configured based on the size of theactive subband.

The present disclosure provides communication methods for low-costterminals to allow LTE terminals and low-cost terminals to efficientlyco-exist in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a basic structure of time-frequency domainwhich is radio resource domain where the data or control channel istransmitted on downlink in the LTE system;

FIG. 2 is a view illustrating an operation example of subframes in a TDDframe;

FIG. 3 is a view illustrating another operation example of subframes ina TDD frame;

FIG. 4 is a view illustrating a problematic situation to be solvedaccording to the present disclosure;

FIG. 5 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 6a is a flowchart illustrating an operation by a base station for acontrol channel transmission method according to an embodiment of thepresent disclosure;

FIG. 6b is a flowchart illustrating an operation by a terminal for acontrol channel transmission method according to an embodiment of thepresent disclosure;

FIG. 7 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 8a is a view illustrating a method for transmitting a controlchannel by a base station according to an embodiment of the presentdisclosure;

FIG. 8b is a view illustrating a method for transmitting a controlchannel by a terminal according to an embodiment of the presentdisclosure;

FIG. 9 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 10a is a flowchart illustrating an operation by a base station fora control channel transmission method according to an embodiment of thepresent disclosure;

FIG. 10b is a flowchart illustrating an operation by a terminal for acontrol channel transmission method according to an embodiment of thepresent disclosure;

FIG. 11 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 12 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 13 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 14 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure;

FIG. 15a is a view illustrating a communication network including an LAAcell to which the present disclosure applies;

FIG. 15b is a view illustrating a communication network including an LAAcell to which the present disclosure applies;

FIG. 16 is a view illustrating a method for transmitting channelinformation by grouping serving cells according to an embodiment of thepresent disclosure;

FIG. 17 is a view illustrating a method for communicating periodicchannel information by a base station and a terminal according to anembodiment of the present disclosure;

FIG. 18 is a concept view illustrating an example of configuring andoperating subband where the low-cost terminal operates within the systemtransmission bandwidth according to an embodiment of the presentdisclosure;

FIG. 19 is a concept view illustrating an example in which DCI size isvaried depending on the type of terminal according to an embodiment ofthe present disclosure;

FIG. 20 is a view illustrating a scheduling procedure by a base stationwhen a normal LTE terminal and a low-cost terminal co-exist in the samesystem according to an embodiment of the present disclosure;

FIG. 21 is a view illustrating a procedure of obtaining DCI by alow-cost terminal operating according to an embodiment of the presentdisclosure;

FIG. 22 is a concept view illustrating an example of operating withoutexplicitly configuring a subband where a low-cost terminal operates in asystem transmission bandwidth according to an embodiment of the presentdisclosure;

FIG. 23 is a concept view illustrating a method for determining a DCIsize according to an embodiment of the present disclosure;

FIG. 24 is a view illustrating a scheduling procedure by a base stationwhen a normal LTE terminal and a low-cost terminal co-exist in the samesystem according to an embodiment of the present disclosure;

FIG. 25 is a view illustrating a procedure of obtaining DCI by alow-cost terminal operating according to an embodiment of the presentdisclosure;

FIG. 26 is a concept view illustrating an example of previouslyconfiguring and dynamically varying a subband where a low-cost terminaloperates in a system transmission bandwidth according to an embodimentof the present disclosure;

FIG. 27 is a concept view illustrating an example of a method forindicating a subband in an FDD system according to an embodiment of thepresent disclosure;

FIG. 28 is a view illustrating an exemplary configuration of a basestation for implementing an embodiment of the present disclosure; and

FIG. 29 is a view illustrating an exemplary configuration of a terminalfor implementing an embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure are described indetail with reference to the accompanying drawings. When determined tomake the subject matter of the present disclosure unclear, the detailedof the known functions or configurations may be skipped. The terms asused herein are defined considering the functions in the presentdisclosure and may be replaced with other terms according to theintention or practice of the user or operator. Therefore, the termsshould be defined based on the overall disclosure.

Hereinafter, according to this disclosure, the long term evolution (LTE)system and the LTE-advanced (LTE-A) system are described as examples,but the present disclosure may also apply to other communication systemsadopting base station scheduling without limited thereto. Thedescription of embodiments of the present disclosure primarily targetsadvanced E-UTRA (or LTE-A) supporting carrier aggregation but thesubject matter of the present disclosure may also be applicable to othercommunication systems with a similar technical background with minorchanges without significantly departing from the scope of the presentdisclosure, and this may be possible under the determination of thoseskilled in the art to which the present disclosure pertains. Forexample, the subject matter of the present disclosure may be applicableto multicarrier HSPA supporting carrier aggregation.

Before detailing the present disclosure, some terms as used herein maybe interpreted as follows, for example. However, it should be noted thatthe present disclosure is not limited thereto.

The base station is an entity communicating with a UE and may be denotedBS, NodeB (NB), eNodeB (eNB), or AP (Access Point).

The user equipment is an entity communicating with a base station, maybe denoted UE, mobile station (MS), mobile equipment (ME), device, orterminal.

Reference signal (RS) is a signal that enables the terminal to estimatechannel, and this reference signal may be received from the basestation. The reference signals for the LTE communication system includethe common reference signal (CRS) and the demodulation reference signal(DMRS), a dedicated reference signal.

The CRS is a reference signal transmitted over the overall downlink bandand receivable by all the UEs and is used for channel estimation,configuring feedback information by the UE, and demodulation of datachannel. The DMRS is a reference signal transmitted over the overalldownlink band. The DMRS is used for demodulation of a data channel by aparticular UE and channel estimation, but not used for configuringfeedback information unlike the CRS. Accordingly, the DMRS istransmitted through a PRB resource that is to be scheduled by the UE.

HARQ-ACK signal refers to an acknowledge (ACK) or negative ACK (HACK)signal transmitted in the HARQ procedure and is simply referred to as‘HARQ-ACK.’

Hereinafter, according to the present disclosure, a scheme forsupporting repetitive transmission by a low-cost terminal is describedwith reference to FIGS. 2 to 14, a periodic channel informationtransmission scheme in a system supporting multiple serving cells isdescribed in connection with FIGS. 15 to 17, a resource allocation andcommunication scheme by a low-cost terminal is described in connectionwith FIGS. 18 to 27, and devices for supporting embodiments of thepresent disclosure are described in connection with FIGS. 28 and 29.

In LTE TDD system, first, the uplink/downlink timing relation ofphysical downlink shared channel (PDSCH), which is a physical channelfor downlink data transmission, and its corresponding physical uplinkcontrol channel (PUCCH) or physical uplink shared channel (PUSCH) whichis a physical channel through which uplink HARQ ACK/NACK is transmittedis as follows.

The terminal, if receiving PDSCH that has been transmitted in subframen-k from the base station, may transmit uplink HARQ ACK/NACK for thePDSCH in uplink subframe n. Here, k is a component of set K, and K isdefined in Table 3.

TABLE 3 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4 —— 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6— — 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7, 11 6, 5, 4, 7 — —— — — — 5 — — 13, 12, 9, 8, 7, 5, 4, 11, 6 — — — — — — — 6 — — 7 7 5 — —7 7 —

Table 4 re-summarizes, according to the definitions in Table 3,subframes where uplink HARQ ACK/NACK is transmitted for PDSCH when thePDSCH is transmitted in each downlink subframe (D) or special subframe(S) n in each TDD UL-DL configuration.

TABLE 4 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 D S U U U DS U U U 4 6 4 6 1 D S U U D D S U U D 7 6 4 7 6 4 2 D S U D D D S U D D7 6 4 8 7 6 4 8 3 D S U U U D D D D D 4 11 7 6 6 5 5 4 D S U U D D D D DD 12 6 8 7 7 6 5 4 5 D S U D D D D D D D 12 6 9 8 7 6 5 4 13 6 D S U U DD S U U D 7 7 8 7 7 5

FIG. 2 is a view illustrating an operation example of subframes in a TDDframe.

Table 4 is described below with reference to FIG. 2. Here, FIG. 2 is aview exemplifying, as per the definitions in Table 4, the subframe whereuplink HARQ ACK/NACK corresponding to PDSCH is transmitted when thePDSCH is transmitted in each downlink or special subframe in TDD UL-DLconfiguration #6 of Table 4.

For example, the uplink HARQ ACK/NACK corresponding to the PDSCH 201transmitted from the base station in subframe #0 211 of radio frame i istransmitted by the terminal in subframe #7 of radio frame i (203). Here,the downlink control information DCI including scheduling information onPDSCH 201 is transmitted through PDCCH in the same subframe 211 as thesubframe transmitted where the PDSCH is transmitted. As another example,the uplink HARQ ACK/NACK corresponding to the PDSCH 205 transmitted fromthe base station in subframe #9 215 of radio frame i is transmitted bythe terminal in subframe #4 of radio frame i+1 (207). Likewise, thedownlink control information DCI including scheduling information onPDSCH 205 is transmitted through PDCCH in the same subframe 215 as thesubframe transmitted where the PDSCH is transmitted.

In LTE system, downlink HARQ adopts asynchronous HARQ scheme, which is ascheme where the data retransmission time is not fixed. As used herein,downlink HARQ refers to an HARQ (initial transmission, ACK/NACK, orretransmission) whose transmission direction is downlink. The reason whydownlink HARQ adopts asynchronous HARQ scheme is that not fixingtransmission time would make little trouble even because in the LTE TDDsystem downlink transmission generally use more subframes than uplinktransmission. That is, in case the base station receives feedback ofHARQ NACK from the terminal for the transmitted HARQ initialtransmission data, the base station freely determines the transmissiontime of next HARQ retransmission data by scheduling operation. Theterminal buffers the HARQ data determined to have an error as a resultof determining the received data for HARQ operation and then performscombining with next HARQ retransmission data. Here, in order to maintainthe reception buffer capacity of the terminal within a predeterminedrange, the maximum number of downlink HARQ processes per TDD UL-DLconfiguration is defined as in Table 5. One HARQ process is mapped toone subframe in the time domain.

TABLE 5 TDD UL/DL Maximum number of configuration HARQ processes 0 4 1 72 10 3 9 4 12 5 15 6 6

Referring to the example shown in FIG. 2, the terminal, if determiningthat the PDSCH 201 transmitted from the base station subframe #0 211 ofradio frame i has an error, transmits HARQ NACK in subframe #7 of radioframe i (203). When receiving the HARQ NACK 203, the base station mayconfigure retransmission data for the PDSCH 201 with the PDSCH 209 andtransmit together with PDCCH. Referring to FIG. 2, the maximum number ofdownlink HARQ processes in TDD UL-DL configuration #6 is six as per thedefinitions shown in Table 5 above. That is, there are a total of sixdownlink HARQ processes 211, 222, 213, 214, 215, and 216 between theinitial transmission PDSCH 201 and the retransmission PDSCH 209.

Unlike downlink HARQ, in LTE system, uplink HARQ adopts synchronous HARQscheme, which is a scheme where the data retransmission time is fixed.As used herein, uplink HARQ refers to an HARQ (initial transmission,ACK/NACK, or retransmission) whose transmission direction is downlink.The reason why uplink HARQ adopts synchronous HARQ scheme is that in theLTE TDD system uplink transmission generally use fewer subframes thandownlink transmission, and thus the terminal cannot freely choose anduse uplink resources. That is, the timing relation in uplink/downlinktiming between the physical channel for uplink data transmission, PUSCH(physical uplink shared channel), and its precedent downlink controlchannel, PDCCH, and the physical channel where HARQ ACK/NACKcorresponding to the PUSCH is transmitted, PHICH (physical hybridindicator channel) is fixed by the following rule.

The terminal, when receiving PDCCH including uplink schedulinginformation transmitted from the base station in subframe n or PHICHwhere downlink HARQ ACK/NACK is transmitted from, transmits uplink datacorresponding to the control information through PUSCH in subframe n+k.Here, k is as defined in Table 6.

TABLE 6 TDD UL/DL DL subframe number n Configuration 0 1 2 3 4 5 6 7 8 90 4 6 4 6 1 6 4 6 4 2 4 4 3 4 4 4 4 4 4 5 4 6 7 7 7 7 5

If the terminal receives PHICH carrying downlink HARQ ACK/NACK from thebase station in subframe i, the PHICH corresponds to the PUSCHtransmitted from the terminal in subframe i−k. Here, k is as defined inTable 7.

TABLE 7 TDD UL/DL DL subframe number i Configuration 0 1 2 3 4 5 6 7 8 90 7 4 7 4 1 4 6 4 6 2 6 6 3 6 6 6 4 6 6 5 6 6 6 4 7 4 6

FIG. 3 is a view illustrating an operation example of subframes in a TDDframe. FIG. 3 is a view illustrating an example according to thedefinitions in Tables 6 and 7, as to the subframe where uplink PUSCHcorresponding to PDCCH or PHICH is transmitted when the PDCCH or thePHICH is transmitted in each downlink or special subframe in case of TDDUL-DL configuration #1, and the subframe where PHICH is transmittedcorresponding to the PUSCH.

For example, the uplink PUSCH corresponding to the PDCCH or PHICH 301transmitted from the base station in subframe #1 of radio frame i istransmitted by the terminal in subframe #7(=1+6) of radio frame i (303).The base station transmits the PHICH corresponding to the PUSCH to theterminal in subframe #1 of radio frame i+1 (305). As another example,the uplink PUSCH corresponding to the PDCCH or PHICH 307 transmittedfrom the base station in subframe #6 of radio frame i is transmitted bythe terminal in subframe #2 of radio frame i+1 (309). The base stationtransmits the PHICH corresponding to the PUSCH to the terminal insubframe #6 of radio frame i+1 (311).

Further, LTE TDD system may pose limitations, regarding PUSCHtransmission, the downlink transmission of PDCCH or PHICH correspondingto the PUSCH in a particular downlink subframe, guaranteeing minimumtransmission/reception processing time of base station and terminal. Forexample, in case of TDD UL-DL configuration #1 of Tables 6 and 7, PDCCHfor scheduling the PUSCH or PHICH corresponding to the PUSCH is nottransmitted in subframe #0 #5.

The LTE system operating as above may supportlower-cost/lower-complexity terminals (UEs) by limiting some functionsof the terminal. Such low-cost terminals are anticipated to beappropriate for machine-type communication (MTC) or machine-to-machine(M2M services for remote metering, security, or logistics. Further,low-cost terminals are expected as means to implement cellular-basedInternet of things (cIoT).

For low costs or low complexity, the number of of receive antennas ofterminal may be limited to one, to reduce costs of RF components ofterminal or TBS processable by the present disclosure may be set with anupper cap to reduce costs of data receiving buffer of the terminal.Common LTE terminals are equipped with broadband signal communicationfunctionality for a minimum of 20 MHz band regardless of the systemtransmission bandwidth, and by comparison, low-cost terminals arelimited as having 20 MHz or less maximum bandwidth to leead toadditional cost savings and reduced complexity. For example, in the 20MHz channel bandwidth LTE system, low-cost terminals only supportive of1.4 MHz channel bandwidth may be defined for their operation. Further,low-cost terminals may have limited coverage when they are located at aparticular position, e.g., cell boundary, and for enhanced coverage forlow-cost terminals, repetitive transmission is taken into account. Suchrepetitive transmission is apparently applicable to enhanced coveragefor normal LTE terminals. Here, there is a need for defining HARQcommunication operation for low-cost terminals performing repetitivetransmission in a coverage enhancing mode differentiated from normal LTEterminals with no coverage limit, and a specific method is proposedaccording to the present disclosure.

To achieve the goals set forth above, the following embodiments areproposed.

According to an embodiment of the present disclosure, repetitivetransmission of information for uplink data scheduling to a low-costterminal in a TDD cell is performed (only) in downlink subframes havingan uplink HARQ process defined, and uplink data for the repetitivetransmission is transmitted based on the HARQ timing of the HARQ processdefined in a downlink subframe where the repetitive transmission iscomplete, and HARQ-ACKs for the uplink data may be repeatedlytransmitted based on the HARQ timing of the HARQ process defined in theuplink subframe where the repetitive transmission of uplink data iscomplete.

According to an embodiment of the present disclosure, repetitivetransmission of downlink signals for uplink data scheduling to alow-cost terminal in a TDD cell is performed in all downlink subframes,uplink data is transmitted based on the HARQ timing of the subframewhere the repetitive transmission is complete or the closest downlinksubframe having an uplink HARQ process defined which comes after thedownlink subframe where the repetitive transmission is complete, and theHARQ-ACKs for the uplink data may be transmitted based on the HARQtiming of the HARQ process defined in the uplink subframe where therepetitive transmission of uplink data is complete.

According to an embodiment of the present disclosure, repetitivetransmission for uplink data scheduling to a low-cost terminal in a TDDcell is performed in all downlink subframes, transmission of uplink datais started in the closest (earliest) uplink subframe coming p1 subframesfrom the downlink subframe where the repetitive transmission iscomplete, repetitive transmission of uplink data is performed in allsubsequent uplink subframes, transmission of HARQ-ACKs is started in theclosest downlink subframe coming p2 subframes after the uplink subframewhere the repetitive transmission of the UCI PUSCH data is complete, andHARQ-ACKs may be repeatedly transmitted in all subsequent downlinksubframes.

According to an embodiment of the present disclosure, repetitivetransmission for uplink data scheduling to a low-cost terminal in a TDDcell is transmitted to be complete in the downlink subframe having anuplink HARQ process defined, transmission of uplink data is started inthe uplink subframe according to the HARQ timing of the HARQ processdefined in the downlink subframe where the repetitive transmission iscomplete, repetitive transmission of uplink data is performed in allsubsequent uplink subframes, transmission of HARQ-ACKs is started in thedownlink subframe according to the HARQ timing of the HARQ processdefined in the uplink subframe where repetitive transmission of theuplink data is complete, and HARQ-ACKs may be repeatedly transmitted inall subsequent subframes.

According to an embodiment of the present disclosure, repetitivetransmission for downlink data scheduling to a low-cost terminal in aTDD cell is performed in all downlink subframes, transmission ofdownlink data is started in the closest downlink subframe coming k1subframes after the downlink subframe where the repetitive transmissionis complete, repetitive transmission of downlink data is performed inall subsequent downlink subframes, transmission of HARQ-ACKs is startedin the closest uplink subframe coming k2 subframes after the downlinksubframe where the repetitive transmission of the downlink data iscomplete, and HARQ-ACKs may be repeatedly transmitted in all subsequentuplink subframes.

According to an embodiment of the present disclosure, repetitivetransmission for uplink data scheduling to a low-cost terminal in a FDDcell is performed in all downlink subframes, transmission of uplink datais started in the uplink subframe coming k1 subframes from the downlinksubframe where the repetitive transmission is complete, repetitivetransmission of uplink data is performed in all subsequent uplinksubframes, transmission of HARQ-ACKs is started in the closest downlinksubframe coming k2 subframes after the uplink subframe where therepetitive transmission of the UCI PUSCH data is complete, and HARQ-ACKsmay be repeatedly transmitted in all subsequent downlink subframes.

According to an embodiment of the present disclosure, repetitivetransmission for downlink data scheduling to a low-cost terminal in anFDD cell is performed in all downlink subframes, repetitive transmissionof downlink data is started in the downlink subframe coming ml subframesafter the downlink subframe where the repetitive transmission iscomplete, repetitive transmission of the downlink data is performed inall subsequent downlink subframes, transmission of HARQ-ACKs is startedin the uplink subframe coming k2 subframes after the downlink subframewhere the repetitive transmission of downlink data is complete, andHARQ-ACKs may be repeatedly transmitted in all subsequent uplinksubframes.

FIG. 4 is a view illustrating a problematic situation to be solvedaccording to the present disclosure.

FIG. 4 exemplifies a static TDD-based LTE cell 401.

It is assumed that the terminal (e.g., a low-cost terminal) is alwaysset in coverage enhancing mode, and in case it is set in the coverageenhancing mode, it may communicate data through receptiontransmission/reception. Downlink subframes and uplink subframes areconfigured in the cell 401 according to TDD UL-DL configuration #4. Theterminal may obtain TDD UL-DL configuration for the cell from systeminformation or higher layer information. The coverage enhancing mode ofthe terminal may be set by a higher layer signaling from the basestation, and the terminal always operating in the coverage enhancingmode may signal to the base station that it is always operating in thecoverage enhancing mode.

A TDD-based downlink subframe and uplink subframe configure one HARQprocess. That is, the subframes having such pattern as shown in FIG. 4are subframes configuring one HARQ process. For example, uplink subframe#2 421 and downlink subframe #8 423 configure one uplink HARQ process,and uplink subframe #3 422 and downlink subframe #9 424 configure oneuplink HARQ process.

Further, the terminal receiving uplink scheduling information indownlink subframe #8 423 of radio frame i transmits uplink data inuplink subframe #2 425 of next radio frame (radio frame i+1) based onthe uplink HARQ timing according to the uplink HARQ processconfiguration. Further, the terminal receiving uplink schedulinginformation in downlink subframe #9 424 of radio frame i transmitsuplink data in uplink subframe #3 426 of next radio frame (radio framei+1) based on the uplink HARQ timing according to the uplink HARQprocess configuration.

However, in FIG. 4, downlink subframes #0, #1, #4, #5, #6, and #7 ofradio frame i do not configure uplink HARQ process, and it may be seenthat downlink subframes #0, #1, #4, #5, #6, and #7 have no uplink HARQtiming defined based on uplink HARQ process.

A channel reception method between base station and terminal forrepetitive transmission/reception may be defined depending on channeltypes as follows.

TABLE 8 Channel and signal Receiving method (e)PDCCH Chase Combining(e)PHICH Chase Combining PUSCH Incremental Redundancy PDSCH IncrementalRedundancy PUCCH Chase Combining PRACH Chase Combining PBCH ChaseCombining PSS/SSS Chase Combining SRS Chase Combining CRS/CSI-RS/PRSChase Combining

Configuration information related to repetitive transmission of theterminal, i.e., repetitive transmission start subframe, repetitivetransmission count, or frequency resource information where repetitivetransmission channel is transmitted, may be previously transmitted tothe terminal. In FIG. 4, it is assumed that a total of four times ofrepetitive transmission is set. The base station transmits uplink datascheduling information 411, 412, 413, and 414 to the terminal insubframe #4, subframe #5, subframe #6, and subframe #7. At this time,downlink subframe #7 has not uplink HARQ process defined. Accordingly,the terminal faces the situation where it cannot be aware of the uplinksubframe which uplink data 415 (e.g., PUSCH) for the schedulinginformation 411, 412, 413, and 414 repeatedly transmitted should betransmitted through.

FIG. 5 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 5 exemplifies a static TDD-based LTE cell 501. In the exemplifiedscheme, the base station performs repetitive transmission on the uplinkdata scheduling information (only) in downlink subframes having LTE celluplink HARQ process defined so that the terminal performs uplink HARQtransmission according to the defined uplink HARQ process timing.

It is assumed that the terminal (e.g., a low-cost terminal) is alwaysset in coverage enhancing mode, and in case it is set in the coverageenhancing mode, it may communicate data through receptiontransmission/reception. Downlink subframes and uplink subframes areconfigured in the cell 501 according to TDD UL-DL configuration #1. Theterminal may obtain TDD UL-DL configuration for the cell 501 from systeminformation (e.g., system information block (SIB) information) or higherlayer information (i.e., higher layer signaling). The coverage enhancingmode of the terminal may be set by a higher layer signaling from thebase station, and the terminal always operating in the coverageenhancing mode may signal to the base station that it is alwaysoperating in the coverage enhancing mode. Or, the terminal may setitself to operate in the coverage enhancing mode through reception ofsystem information or a random access procedure or the terminal may beset to operate in the coverage enhancing mode by the base station.

A TDD-based downlink subframe and uplink subframe may configure oneuplink HARQ process. The subframes having such pattern as shown in FIG.5 configure one HARQ process. However, since the number of uplinksubframes is not always the same as the number of downlink subframes,all of the subframes included in one radio frame do not configure HARQprocess. For example, in FIG. 5, downlink subframes #0 and #5 do notconfigure uplink HARQ process, and it may be seen that no uplink HARQtiming is defined for downlink subframes #0 and #5. Accordingly, theHARQ transmission scheme shown in FIG. 5 may advantageously apply to thesituations where the number of downlink subframes configuring no uplinkHARQ process in the radio frame is smaller as compared with other UL-DLconfigurations (i.e., among the UL-DL configurations, ones havingrelatively more downlink subframes configuring HARQ processes). For areason, many of the subframes configuring a radio frame configure uplinkHARQ process, and thus, even when repetitive transmission is performedonly with the subframes configuring the uplink HARQ process, not muchtime is consumed for transmission, and there is no need of specifying anadditional rule for HARQ process, thus leading to minimized influence onthe standards.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal. In FIG. 5, it is assumed thata total of four times of repetitive transmission is set. Although FIG. 5illustrates an example in which the uplink scheduling information,uplink data, and HARQ-ACK are set to have the same number of times ofrepetition, such pieces of information may be set to be different fromeach other by a higher layer signal or may be adjusted to be differentdynamically by an L1 signal.

The base station transmits uplink data scheduling information to theterminal through repetitive transmission in subframe #1, subframe #4,subframe #6, and subframe #9 of radio frame k 502 (511, 512, 513, and514). Subframe #1, subframe #4, subframe #6, and subframe #9 aresubframes having uplink HARQ process defined therein, and the basestation does not perform repetitive transmission in subframe #0 andsubframe #5 having no uplink HARQ process defined.

After repetitive transmission of uplink scheduling information as manytimes as the repetition count as set, the terminal may performrepetitive transmission for uplink data transmission based on the uplinkHARQ timing defined in subframe #9 of radio frame k 502 that is the lastsubframe of repetitive transmission. The subframe forming HARQ processwith subframe #9 of radio frame k 502 is subframe #3. Accordingly, theterminal may perform repetitive transmission on uplink data fromsubframe #3 of radio frame k+1 503 by following the uplink HARQ processdefined in subframe #9 (521). Subsequently, the terminal performsrepetitive transmission on uplink data in subframe #2 of radio frame k+2504 and subframes #7 and #8 of radio frame k+1 503 as many times as theremaining repetition count (522, 523, and 524). Here, it may be seenthat the uplink subframes where uplink data transmission is performedhave uplink HARQ process defined therein (the subframes having a patternas shown in FIG. 5).

Next, repetitive transmission of HARQ-ACKs (through EPDCCH or ePHICH)may be performed from subframe #6 of radio frame k+2 504 according tothe uplink HARQ timing based on the uplink HARQ process defined insubframe #2 of radio frame k+2 504 (531). The HARQ-ACK through ePDCCH orePHICH is an HARQ signal transmitted from the base station for thePUSCHs 521, 522, 523, and 524 transmitted on uplink from the terminal.Subsequently, the base station may perform repetitive transmission ofHARQ-ACKs in subframe #9 of radio frame k+2 504, subframe #1 of radioframe k+3 505, and subframe #4 of radio frame k+3 505 as many times asthe remaining repetition count (532, 533, and 534). Additionally, ifthere is uplink data retransmission, the terminal may perform uplinkdata repetitive transmission based on the uplink HARQ timing defined insubframe #4 of radio frame k+2 504.

As exemplified in FIG. 5, determining the uplink transmission startsubframe based on the subframes where uplink data scheduling informationis transmitted (i.e., determining ePDCCH-to-PUSCH HARQ timing) anddetermining HARQ-ACK transmission start subframe based on the subframeswhere uplink data is transmitted (i.e., determining PUSCH-to-HARQ-ACKtiming) may apply to both the base station and the terminal, or any oneof the ePDCCH-to-PUSCH HARQ timing determination and thePUSCH-to-HARQ-ACK timing determination may apply thereto. For example,since the subframes for downlink HARQ-ACK transmission are notinsufficient in the radio frame (unlike the subframes for uplink datatransmission), a subframe for HARQ-ACK transmission may be dynamicallydetermined by the base station, and in such case, the PUSCH-to-HARQ-ACKtiming determination scheme might not apply.

FIG. 6a is a flowchart illustrating an operation by a base station for acontrol channel transmission method according to an embodiment of thepresent disclosure.

FIG. 6a exemplifies a method for performing repetitive transmission onan uplink HARQ process by a base station as shwon in FIG. 5.

In step 601, the base station transmits information on LTE cell to theterminal, configures repetitive transmission-related information, andtransmits the same to the terminal.

The information on LTE cell may be UL-DL configuration information orspecial subframe configuration information. The information on LTE cellmay be transmitted to the terminal through system information (e.g., SIBinformation) or higher layer information (i.e., higher layer signaling).The repetitive transmission-related information, e.g., repetitivetransmission start subframe, repetitive transmission count, informationon frequency resources for transmitting repetitive transmission channel,or information on groups of (downlink or uplink) subframes whererepetitive transmission may be conducted, may be transmitted to theterminal via system information, higher layer information, or L1 signal.Here, it is assumed that the terminal (e.g., a low-cost terminal) isalways set in coverage enhancing mode, and in case it is set in thecoverage enhancing mode, it may communicate data through receptiontransmission/reception. The coverage enhancing mode of the terminal maybe set by a higher layer signaling from the base station, and theterminal always operating in the coverage enhancing mode may signal tothe base station that it is always operating in the coverage enhancingmode. Or, the terminal may set itself to operate in the coverageenhancing mode through reception of system information or a randomaccess procedure or the terminal may be set to operate in the coverageenhancing mode by the base station.

In step 602, the base station repeatedly transmits the uplink schedulinginformation (only) in downlink subframes having uplink HARQ processdefined based on the configured repetitive transmission-relatedinformation.

In step 603, the base station repeatedly receives uplink data based onthe configured repetitive transmission-related information in the uplinksubframe according to the uplink HARQ timing based on the uplink HARQprocess of the downlink subframe where the repetitive transmission ofuplink scheduling information is complete. Taking an example as shown inFIG. 5, when the base station completes the repetitive transmission ofuplink scheduling information in subframe #9 of radio frame k 502, thesubframe according to the uplink HARQ timing based on the uplink HARQprocess of subframe #9 is subframe #3. Accordingly, the base station maystart repetitive reception from subframe #3 of radio frame k+1 503.

In step 604, the base station repeatedly transmits HARQ-ACKs (throughePDCCH or ePHICH) based on the configured repetitivetransmission-related information in the downlink subframe according tothe uplink HARQ timing based on the uplink HARQ process of the uplinksubframe where the repetitive reception of uplink data is complete.Taking an example as shown in FIG. 5, when the base station completesthe repetitive reception of uplink data in subframe #2 of radio framek+2 504, the downlink subframe according to the uplink HARQ timing basedon the uplink HARQ process of subframe #2 is subframe #6. Accordingly,the base station may start repetitive transmission of HARQ-ACKs fromsubframe #6 of radio frame k+2 504.

FIG. 6b is a flowchart illustrating an operation by a terminal for acontrol channel transmission method according to an embodiment of thepresent disclosure.

FIG. 6b exemplifies a method for performing repetitive transmission onan uplink HARQ process by a terminal as shwon in FIG. 5.

In step 611, the terminal receives information on LTE cell from the basestation and receives repetitive transmission-related informationconfigured by the base station.

The information on LTE cell may be UL-DL configuration information orspecial subframe configuration information. The information on LTE cellmay be received from the base station through system information (e.g.,SIB information) or higher layer information (i.e., higher layersignaling). The repetitive transmission-related configurationinformation, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bereceived from the base station via system information, higher layerinformation, or L1 signal. The repetitive transmission-relatedinformation, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of (downlinkor uplink) subframes where repetitive transmission may be conducted, maybe transmitted to the terminal via system information, higher layerinformation, or L1 signal. Here, it is assumed that the terminal (e.g.,a low-cost terminal) is always set in coverage enhancing mode, and incase it is set in the coverage enhancing mode, it may communicate datathrough reception transmission/reception. The coverage enhancing mode ofthe terminal may be set by a higher layer signaling from the basestation, and the terminal always operating in the coverage enhancingmode may signal to the base station that it is always operating in thecoverage enhancing mode. Or, the terminal may set itself to operate inthe coverage enhancing mode through reception of system information or arandom access procedure or the terminal may be set to operate in thecoverage enhancing mode by the base station.

In step 612, the terminal repeatedly receives uplink schedulinginformation based on the received repetitive transmission-relatedinformation in (only) downlink subframes having the uplink HARQ processdefined.

In step 613, the terminal repeatedly transmits uplink data based on thereceived repetitive transmission-related information in the uplinksubframe according to the uplink HARQ timing based on the uplink HARQprocess of the downlink subframe where the repetitive reception ofuplink scheduling information is complete. Taking an example as shown inFIG. 5, when the terminal completes the repetitive reception of uplinkscheduling information in subframe #9 of radio frame k 502, the subframeaccording to the uplink HARQ timing based on the uplink HARQ process ofsubframe #9 is subframe #3. Accordingly, the terminal may startrepetitive transmission of uplink data from subframe #3 of radio framek+1 503.

In step 614, the terminal repeatedly receives HARQ-ACKs (through ePDCCHor ePHICH) based on the received repetitive transmission-relatedinformation in the downlink subframe according to the uplink HARQ timingbased on the uplink HARQ process of the uplink subframe where therepetitive transmission of uplink data is complete. Taking an example asshown in FIG. 5, when the terminal completes the repetitive transmissionof uplink data in subframe #2 of radio frame k+2 504, the downlinksubframe according to the uplink HARQ timing based on the uplink HARQprocess of subframe #2 is subframe #6. Accordingly, the terminal maystart repetitive reception of HARQ-ACKs from subframe #6 of radio framek+2 504.

FIG. 7 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 7 exemplifies a static TDD-based LTE cell 701. The base station mayperform repetitive transmission of uplink data scheduling information inall the downlink subframes regardless of the uplink HARQ process definedin the LTE cell. Accordingly, according to this embodiment, there isexemplified a scheme in which a new uplink HARQ timing is defined, andthe base station and the terminal performs uplink HARQ communicationaccording to the new uplink HARQ timing.

It is assumed that the terminal (e.g., a low-cost terminal) is alwaysset in coverage enhancing mode, and in case it is set in the coverageenhancing mode, it may communicate data through receptiontransmission/reception. Downlink subframes and uplink subframes areconfigured in the cell 701 according to TDD UL-DL configuration #2. Theterminal may obtain TDD UL-DL configuration for the cell 501 from systeminformation (e.g., SIB information) or higher layer information (i.e.,higher layer signaling). The coverage enhancing mode of the terminal maybe set by a higher layer signaling from the base station, and theterminal always operating in the coverage enhancing mode may signal tothe base station that it is always operating in the coverage enhancingmode. Or, the terminal may set itself to operate in the coverageenhancing mode through reception of system information or a randomaccess procedure or the terminal may be set to operate in the coverageenhancing mode by the base station.

A TDD-based downlink subframe and uplink subframe may configure oneuplink HARQ process. The subframes having such pattern as shown in FIG.7 configure one HARQ process. In FIG. 7, downlink subframes #0, #1, #4,#5, #6, and #9 of radio frame i do not configure uplink HARQ process,and it may be seen that subframes #0, #1, #4, #5, #6, and #9 have nouplink HARQ timing defined based on uplink HARQ process. Accordingly,the HARQ transmission scheme shown in FIG. 7 may advantageously apply tothe situations where the number of downlink subframes configuring nouplink HARQ process in the radio frame is larger as compared with otherUL-DL configurations (i.e., among the UL-DL configurations, ones havingrelatively fewer downlink subframes configuring HARQ processes). For areason, many of the subframes configuring a radio frame do not configureuplink HARQ process, and thus, it would take long to perform repetitivetransmission only with the subframes configuring uplink HARQ process.Accordingly, it is advantageous in minimizing transmission time toperform repetitive transmission in all the downlink subframes regardlessof whether HARQ process is configured in the example shown in FIG. 7,and there is a need of introducing a new uplink HARQ timing. Althoughthe introduction of such new uplink HARQ timing might influence thestandards, it would be advantageous in leading to minimized transmissiontime to perform repetitive transmission in all the downlink subframes inthe example shown in FIG. 7.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal.

A group of uplink or downlink subframes may be a group of downlinksubframes for transmission of, e.g., uplink or downlink scheduling. Ifthe repetitive transmission-related information is transmitted to theterminal and configured, the terminal may attempt to detect PDCCH (orePDCCH) for uplink or downlink scheduling only in at least one downlinksubframe in the group of downlink subframes. Further, the terminal mayalso try to detect PDCCH (or ePDCCH) for uplink or downlink schedulingonly in at least one downlink subframe within the group of downlinksubframes also for the PDCCH (or ePDCCH) for scheduling retransmissiondata after repetitive transmission of uplink data by the uplinkscheduling or repetitive transmission of downlink data by downlinkscheduling.

In FIG. 7, it is assumed that a total of four times of repetitivetransmission is set. Although the instant embodiment illustrates anexample in which the uplink scheduling information, uplink data, andHARQ-ACK are set to have the same number of times of repetition, suchpieces of information may be set to be different from each other by ahigher layer signal or may be adjusted to be different dynamically by anL1 signal.

The base station transmits uplink data scheduling information to theterminal through repetitive transmission in subframe #1, subframe #3,subframe #4, and subframe #5 of radio frame k 702 (711, 712, 713, and714). Although FIG. 7 illustrates an example in which uplink schedulinginformation is transmitted in consecutive downlink subframes, repetitivetransmission of uplink scheduling information may also be performed onlyin the downlink subframes configured by the higher signal in the groupof downlink subframes where repetitive transmission may be performed.

Since the repetitive transmission of scheduling information has beencomplete in downlink subframe #5 of radio frame k 702 which has nouplink HARQ process defined, there is a need of defining a new uplinkHARQ transmission timing in downlink subframe #5. In the instantembodiment, the base station or the terminal may determine uplink HARQtransmission timing under the assumption that the repetitivetransmission has been complete in subframe #5 or the closest (orearliest coming) downlink subframe coming after subframe #5 and havingan uplink HARQ process defined and may perform uplink data transmissionbased on the determined HARQ transmission timing (715).

Referring to FIG. 7, the repetitive transmission of schedulinginformation (ePDCCH) is complete in the downlink subframe having nouplink HARQ process defined, like subframe #5. The terminal starts therepetitive transmission of uplink data in subframe #2 of radio frame k+1703 according to the HARQ transmission timing of subframe #8 under theassumption that the repetitive transmission has been complete in theclosest subframe (i.e., subframe #8 of radio frame k 702) of thedownlink subframes having uplink HARQ process defined and coming aftersubframe #5 (721). However, if the repetitive transmission of thescheduling information is complete in the subframe (e.g., subframe #3 orsubframe #8) having an uplink HARQ process defined, the terminal may beable to perform uplink data transmission based on the HARQ transmissiontiming in the subframe where it has been complete. Subsequently, theterminal performs uplink data transmission in subframe #7 of radio framek+1 703, subframe #2 of radio frame k+2 704, and subframe #7 of radioframe k+2 704 to perform repetitive transmission as many as therepetition count as set (i.e., four times) (722, 723, and 724). Here,the uplink subframes where uplink data transmission is performed arealways subframes having uplink HARQ process defined therein.

Next, repetitive transmission of HARQ-ACKs (through EPDCCH or ePHICH) isstarted from the subframe according to the uplink HARQ timing based onthe uplink HARQ process defined in subframe #7 of radio frame k+2 704(i.e., subframe #3 of radio frame k+3 705) (731). That is, the basestation performs HARQ-ACK repetitive transmission from subframe #3 ofradio frame k+3 705 (731). The base station performs HARQ-ACKtransmission in subframe #4, subframe #5, and subframe #6 of radio framek+3 705 (732, 733, and 734). Alternatively, repetitive transmission ofHARQ-ACKs (through ePDCCH or ePHICH) may be performed from the closestsubframe in the group of downlink subframes where repetitivetransmission may be performed, as configured by a higher signal, amongthe subframes coming after subframe #3 as per the uplink HARQ timingbased on the uplink HARQ process, and the terminal may perform detectionon the HARQ-ACKs only in some subframes of the subframe group.

If there is additional uplink data retransmission, the terminal mayperform uplink data retransmission. Since no HARQ process is defined insubframe #6 of radio frame k+3 705, the terminal should determine theHARQ timing for retransmission. Here, the terminal may perform uplinkdata retransmission based on the uplink HARQ timing according to theuplink HARQ process of the closest downlink subframe under theassumption that the repetitive transmission of HARQ-ACKs 734 has beencomplete in the closest downlink subframe (i.e., subframe #8 of radioframe k+3 705) having an uplink HARQ process defined and coming aftersubframe #6 of radio frame k+3 705. That is, the terminal may repeatedlyperform uplink data retransmission based on the uplink HARQ timing ofsubframe #8 (i.e., in subframe #2 of the next radio frame) under theassumption that HARQ-ACK (ePDCCH or ePHICH) transmission has beencomplete in subframe #8.

As exemplified in FIG. 7, determining the uplink transmission startsubframe based on the subframes where uplink data scheduling informationis transmitted (determining ePDCCH-to-PUSCH HARQ timing) and determiningHARQ-ACK transmission start subframe based on the subframes where uplinkdata is transmitted (i.e., determining PUSCH-to-HARQ-ACK timing) mayapply to both the base station and the terminal, or any one of theePDCCH-to-PUSCH HARQ timing determination and the PUSCH-to-HARQ-ACKtiming determination may apply thereto. For example, since the subframesfor downlink HARQ-ACK transmission are not insufficient in the radioframe (unlike the subframes for uplink data transmission), a subframefor HARQ-ACK transmission may be dynamically determined by the basestation, and in such case, the PUSCH-to-HARQ-ACK timing determinationscheme might not apply.

FIG. 8a is a view illustrating a method for transmitting a controlchannel by a base station according to an embodiment of the presentdisclosure.

FIG. 8a exemplifies operations by the base station to perform repetitivetransmission on uplink HARQ process shown in FIG. 7.

In step 801, the base station transmits information on LTE cell to theterminal, configures repetitive transmission-related information, andtransmits the same to the terminal.

The information on LTE cell may be UL-DL configuration information andspecial subframe configuration information. The information on LTE cellmay be transmitted to the terminal through system information (e.g., SIBinformation) or higher layer information (i.e., higher layer signaling).The repetitive transmission-related information, e.g., repetitivetransmission start subframe, repetitive transmission count, informationon frequency resources for transmitting repetitive transmission channel,or information on groups of (downlink or uplink) subframes whererepetitive transmission may be conducted, may be transmitted to theterminal via system information, higher layer information, or L1 signal.Here, it is assumed that the terminal (e.g., a low-cost terminal) isalways set in coverage enhancing mode, and in case it is set in thecoverage enhancing mode, it may communicate data through receptiontransmission/reception. The coverage enhancing mode of the terminal maybe set by a higher layer signaling from the base station, and theterminal always operating in the coverage enhancing mode may signal tothe base station that it is always operating in the coverage enhancingmode. Or, the terminal may set itself to operate in the coverageenhancing mode through reception of system information or a randomaccess procedure or the terminal may be set to operate in the coverageenhancing mode by the base station.

In step 802, the base station repeatedly transmits uplink schedulinginformation based on the configured repetitive transmission-relatedinformation in all the downlink subframes or downlink subframes in agroup of downlink subframes where the configured repetitive transmissionmay be performed by a higher layer signal.

In step 803, the base station determines whether uplink HARQ process isdefined in the downlink subframe where repetitive transmission of uplinkscheduling information is complete. If the uplink HARQ process isdefined, the base station repeatedly receives uplink data based on theconfigured repetitive transmission-related information from the uplinksubframe according to the uplink HARQ timing based on the uplink HARQprocess in step 804. In step 805, the base station repeatedly transmitsHARQ-ACKs (through ePDCCH or ePHICH) based on the configured repetitivetransmission-related information in the downlink subframe according tothe uplink HARQ timing based on the uplink HARQ process of the uplinksubframe where the repetitive reception of uplink data is complete.Alternatively, in step 805, the base station may repeatedly transmitHARQ-ACKs (through ePDCCH or ePHICH) based on the configured repetitivetransmission-related information from the closest subframe in the groupof downlink subframes where the configured repetitive transmission maybe performed by a higher layer signal among the subframes coming afterthe downlink subframe according to the uplink HARQ timing based on theuplink HARQ process.

If the uplink HARQ process is not defined, the base station repeatedlyreceives uplink data based on the configured repetitivetransmission-related information in the uplink subframe according to theuplink HARQ timing based on the uplink HARQ process of the closestdownlink subframe having an uplink HARQ process defined and coming afterthe downlink subframe where the repetitive transmission of uplinkscheduling information is complete, in step 806. In step 807, the basestation repeatedly transmits HARQ-ACKs (through ePDCCH or ePHICH) basedon the configured repetitive transmission-related information in thedownlink subframe according to the uplink HARQ timing based on theuplink HARQ process of the uplink subframe where the repetitivereception of uplink data is complete. Alternatively, in step 807, thebase station may repeatedly transmit HARQ-ACKs (through ePDCCH orePHICH) as specified in the configured repetitive transmission-relatedinformation from the closest subframe in the group of downlink subframeswhere the configured repetitive transmission may be performed by ahigher layer signal among the subframes coming after the downlinksubframe according to the uplink HARQ timing based on the uplink HARQprocess.

FIG. 8b is a view illustrating a method for transmitting a controlchannel by a terminal according to an embodiment of the presentdisclosure.

FIG. 8b exemplifies operations by the terminal to perform repetitivetransmission on uplink HARQ process shown in FIG. 7.

In step 811, the terminal receives information on LTE cell from the basestation and receives repetitive transmission-related configurationinformation configured by the base station.

The information on LTE cell may be UL-DL configuration information andspecial subframe configuration information. The information on LTE cellmay be received from the base station through system information (e.g.,SIB information) or higher layer information (i.e., higher layersignaling). The repetitive transmission-related information, e.g.,repetitive transmission start subframe, repetitive transmission count,information on frequency resources for transmitting repetitivetransmission channel, or information on groups of (downlink or uplink)subframes where repetitive transmission may be conducted, may betransmitted to the terminal via system information, higher layerinformation, or L1 signal. Here, it is assumed that the terminal (e.g.,a low-cost terminal) is always set in coverage enhancing mode, and incase it is set in the coverage enhancing mode, it may communicate datathrough reception transmission/reception. The coverage enhancing mode ofthe terminal may be set by a higher layer signaling from the basestation, and the terminal always operating in the coverage enhancingmode may signal to the base station that it is always operating in thecoverage enhancing mode. Or, the terminal may set itself to operate inthe coverage enhancing mode through reception of system information or arandom access procedure or the terminal may be set to operate in thecoverage enhancing mode by the base station.

In step 812, the terminal repeatedly receives uplink schedulinginformation based on the received repetitive transmission-relatedinformation in all the downlink subframes or downlink subframes in agroup of downlink subframes where the configured repetitive transmissionmay be performed by a higher layer signal.

In step 813, the terminal determines whether uplink HARQ process isdefined in the downlink subframe where repetitive transmission of uplinkscheduling information is complete. If the uplink HARQ process isdefined, the terminal repeatedly transmits uplink data based on thereceived repetitive transmission-related information from the uplinksubframe according to the uplink HARQ timing based on the uplink HARQprocess in step 814. In step 815, the terminal repeatedly receivesHARQ-ACKs (through ePDCCH or ePHICH) as specified in the receivedrepetitive transmission-related information in the downlink subframeaccording to the uplink HARQ timing based on the uplink HARQ process ofthe uplink subframe where the repetitive transmission of uplink data iscomplete. Alternatively, in step 815, the terminal may repeatedlyreceive HARQ-ACKs (through ePDCCH or ePHICH) as specified in thereceived repetitive transmission-related information from the closestsubframe in the group of downlink subframes where the configuredrepetitive transmission may be performed by a higher layer signal amongthe subframes coming after the downlink subframe according to the uplinkHARQ timing based on the uplink HARQ process.

If the uplink HARQ process is not defined, the terminal repeatedlytransmits uplink data as specified in the received repetitivetransmission-related information in the uplink subframe according to theuplink HARQ timing based on the uplink HARQ process of the closestdownlink subframe having an uplink HARQ process defined and coming afterthe downlink subframe where the repetitive transmission of uplinkscheduling information is complete, in step 816. In step 817, theterminal repeatedly receives HARQ-ACKs (through ePDCCH or ePHICH) asspecified in the received repetitive transmission-related information inthe downlink subframe according to the uplink HARQ timing based on theuplink HARQ process of the uplink subframe where the repetitivetransmission of uplink data is complete. Alternatively, in step 817, theterminal may repeatedly receive HARQ-ACKs (through ePDCCH or ePHICH) asspecified in the received repetitive transmission-related informationfrom the closest subframe in the group of downlink subframes where theconfigured repetitive transmission may be performed by a higher layersignal among the subframes coming after the downlink subframe accordingto the uplink HARQ timing based on the uplink HARQ process.

FIG. 9 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 9 exemplifies a static TDD-based LTE cell 901. The base station mayperform repetitive transmission of uplink data scheduling information inall the downlink subframes regardless of the uplink HARQ process definedin the LTE cell. Accordingly, according to this embodiment, there isexemplified a scheme in which a new uplink HARQ timing is defined, andthe base station and the terminal performs uplink HARQ communicationaccording to the new uplink HARQ timing.

It is assumed that the terminal (e.g., a low-cost terminal) is alwaysset in coverage enhancing mode, and in case it is set in the coverageenhancing mode, it may communicate data through receptiontransmission/reception. Downlink subframes and uplink subframes areconfigured in the cell 901 according to TDD UL-DL configuration #2. Theterminal may obtain TDD UL-DL configuration for the cell from systeminformation (e.g., SIB information) or higher layer information (i.e.,higher layer signaling). The coverage enhancing mode of the terminal maybe set by a higher layer signaling from the base station, and theterminal always operating in the coverage enhancing mode may signal tothe base station that it is always operating in the coverage enhancingmode. Or, the terminal may set itself to operate in the coverageenhancing mode through reception of system information or a randomaccess procedure or the terminal may be set to operate in the coverageenhancing mode by the base station.

A TDD-based downlink subframe and uplink subframe may configure oneuplink HARQ process. The subframes having such pattern as shown in FIG.9 configure one HARQ process. In FIG. 9, downlink subframes #0, #1, #4,#5, #6, and #9 of radio frame i do not configure uplink HARQ process,and it may be seen that subframes #0, #1, #4, #5, #6, and #9 have nouplink HARQ timing defined based on uplink HARQ process. Accordingly,the HARQ transmission scheme shown in FIG. 9 may advantageously apply tothe situations where the number of downlink subframes configuring nouplink HARQ process in the radio frame is larger as compared with otherUL-DL configurations (i.e., among the UL-DL configurations, ones havingrelatively fewer downlink subframes configuring HARQ processes). For areason, many of the subframes configuring a radio frame do not configureuplink HARQ process, and thus, it would take long to perform repetitivetransmission only with the subframes configuring uplink HARQ process.Accordingly, it is advantageous in minimizing transmission time toperform repetitive transmission in all the downlink subframes regardlessof whether HARQ process is configured in the example shown in FIG. 9,and there is a need of introducing a new uplink HARQ timing. Althoughthe introduction of such new uplink HARQ timing might influence thestandards, it would be advantageous in leading to minimized transmissiontime to perform repetitive transmission in all the downlink subframes inthe example shown in FIG. 9.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal.

A group of uplink or downlink subframes may be a group of downlinksubframes for transmission of, e.g., uplink or downlink scheduling. Ifthe repetitive transmission-related information is transmitted to theterminal and configured, the terminal may attempt to detect PDCCH (orePDCCH) for uplink or downlink scheduling only in at least one downlinksubframe in the group of downlink subframes. Further, the terminal mayalso try to detect PDCCH (or ePDCCH) for uplink or downlink schedulingonly in at least one downlink subframe within the group of downlinksubframes also for the PDCCH (or ePDCCH) for scheduling retransmissiondata after repetitive transmission of uplink data by the uplinkscheduling or repetitive transmission of downlink data by downlinkscheduling.

In FIG. 9, it is assumed that a total of four times of repetitivetransmission is set. Although the instant embodiment illustrates anexample in which the uplink scheduling information, uplink data, andHARQ-ACK are set to have the same number of times of repetition, suchpieces of information may be set to be different from each other. by ahigher layer signal or may be adjusted to be different dynamically by anL1 signal.

The base station transmits uplink data scheduling information to theterminal through repetitive transmission in subframe #1, subframe #3,subframe #4, and subframe #5 of radio frame k 902 (911, 912, 913, and914). Although FIG. 9 illustrates an example in which uplink schedulinginformation is transmitted in consecutive downlink subframes, repetitivetransmission of uplink scheduling information may also be performed onlyin the downlink subframes configured by the higher signal in the groupof downlink subframes where repetitive transmission may be performed.

In FIG. 9, repetitive transmission of uplink scheduling information hasbeen complete in subframe #5, and the terminal may perform repetitivetransmission of uplink data from the closest uplink subframe (i.e.,subframe coming earliest) among uplink subframes coming after apredetermined number (i.e., p1) of subframes. p1 may be set as one ofmultiple values by a higher layer signal (higher layer signaling) or maybe fixed to a particular value by a standard (an agreement previouslydefined). For example, p1 may be fixed to 4. Here, repetitivetransmission of uplink data by the terminal may be initiated from theclosest uplink subframe coming p1 subframes after subframe #5 of radioframe k 902, i.e., subframe #2 of radio frame k+1 903 (921).

That is, in the embodiment shown in FIG. 9, the terminal performs uplinkdata transmission in the closest uplink subframe coming after p1subframes after the downlink subframe where the repetitive transmissionis complete, regardless of whether the uplink HARQ process is defined inthe subframe where repetitive transmission is complete. Althoughrepetitive transmission of uplink data scheduling is complete insubframes having uplink HARQ process defined like subframe #3 orsubframe #8, the terminal may perform uplink data transmission in theuplink subframe first coming p1 subframes after the subframe where it iscomplete regardless of the defined HARQ process.

After the repetitive transmission 921 of uplink data is started by theterminal in subframe #2 of radio frame k+1 903, the terminal performsuplink data repetitive transmission as many times as the repetitioncount as set. That is, the terminal performs uplink data repetitivetransmission in subframe #7 of radio frame k+1 903 and subframe #2 andsubframe #7 of radio frame k+2 904 (922, 923, and 924).

Next, repetitive transmission of HARQ-ACKs (through ePDCCH or ePHICH) isperformed from subframe #1 of radio frame k+3 905, which is the closestdownlink subframe coming a predetermined number (i.e., p2) subframesafter subframe #7 of radio frame k+2 904.

Alternatively, repetitive transmission of HARQ-ACKs (ePDCCH or ePHICH)may also be performed from the closest subframe in the group of downlinksubframes where the configured repetitive transmission may be performedby a higher layer signal among the subframes coming p2 subframes aftersubframe #7. Here, the terminal may detect HARQ-ACK (ePDCCH or ePHICH)in the subframes within the group of downlink subframes. p2 may be setas one of multiple values by a higher layer signal (higher layersignaling) or may be fixed to a particular value by a standard (anagreement previously defined). For example, p2 may be fixed to 4. Here,repetitive transmission of HARQ-ACKs (ePDCCH or ePHICH) by the terminalmay be initiated from the closest downlink subframe coming p2 subframesafter subframe #5 of radio frame k+2 904, i.e., subframe #1 of radioframe k+3 905 (931).

After the repetitive transmission (931) of HARQ-ACKs (ePDCCH or ePHICH)is initiated by the base station in subframe #1 of radio frame k+3 905,the base station performs repetitive transmission of HARQ-ACKs (ePDCCHor ePHICH) in subframe #3, subframe #4, and subframe #5 of radio framek+3 905 as many times as the repetition count as set (932, 933, and934).

Additionally, if there is retransmission of uplink data, the repetitivetransmission of uplink data may be performed in the closest uplinksubframe coming p1 subframes after subframe #5 of radio frame k+3 905.As described in connection with FIG. 9, determining the uplinktransmission start subframe based on the subframes where uplink datascheduling information is transmitted (determining ePDCCH-to-PUSCH HARQtiming) and determining HARQ-ACK transmission start subframe based onthe subframes where uplink data is transmitted (i.e., determiningPUSCH-to-HARQ-ACK timing) may apply to both the base station and theterminal, or any one of the ePDCCH-to-PUSCH HARQ timing determinationand the PUSCH-to-HARQ-ACK timing determination may apply thereto. Forexample, the ePDCCH-to-PUSCH HARQ timing determination may apply whilethe PUSCH-to-HARQ-ACK timing determination does not.

FIG. 10a is a flowchart illustrating an operation by a base station fora control channel transmission method according to an embodiment of thepresent disclosure.

FIG. 10a exemplifies operations by the base station to performrepetitive transmission on uplink HARQ process shown in FIG. 9.

In step 1001, the base station transmits information on LTE cell to theterminal and configures and transmits at least one of repetitivetransmission-related information and HARQ timing information to theterminal.

The information on LTE cell may be UL-DL configuration information andspecial subframe configuration information. The information on LTE cellmay be transmitted to the terminal through system information (e.g., SIBinformation) or higher layer information (i.e., higher layer signaling).The repetitive transmission-related information, e.g., repetitivetransmission start subframe, repetitive transmission count, informationon frequency resources for transmitting repetitive transmission channel,or information on groups of (downlink or uplink) subframes whererepetitive transmission may be conducted, may be transmitted to theterminal via system information, higher layer information, or L1 signal.The HARQ timing information may be information indicating p1 and p2 asshown in FIG. 9, and this information may be transmitted through systeminformation (e.g., SIB information) or higher layer information (i.e.,higher layer signaling). Alternatively, the HARQ timing information maybe fixed to a particular following the standard, and in such case, thisinformation might not be transmitted to the terminal. It is assumed thatthe terminal (e.g., a low-cost terminal) is always set in coverageenhancing mode, and in case it is set in the coverage enhancing mode, itmay communicate data through reception transmission/reception. Thecoverage enhancing mode of the terminal may be set by a higher layersignaling from the base station, and the terminal always operating inthe coverage enhancing mode may signal to the base station that it isalways operating in the coverage enhancing mode. Or, the terminal mayset itself to operate in the coverage enhancing mode through receptionof system information or a random access procedure or the terminal maybe set to operate in the coverage enhancing mode by the base station.

In step 1002, the base station repeatedly transmits uplink schedulinginformation based on the configured repetitive transmission-relatedinformation in all the downlink subframes or downlink subframes in agroup of downlink subframes where the configured repetitive transmissionmay be performed by a higher layer signal.

In step 1003, the base station repeatedly receives uplink data based onthe configured repetitive transmission-related information in theclosest uplink subframe coming p1 subframes after the downlink subframewhere the repetitive transmission of uplink scheduling information iscomplete.

In step 1004, the base station repeatedly transmits HARQ-ACKs (ePDCCH orePHICH) based on the configured repetitive transmission-relatedinformation in the closest subframe within the group of downlinksubframes where the configured repetitive transmission may be performedby a higher layer signal among the subframes coming after the p2subframes or the closest downlink subframe coming p2 subframes after theuplink subframe where the repetitive reception of uplink data iscomplete.

FIG. 10b is a flowchart illustrating an operation by a terminal for acontrol channel transmission method according to an embodiment of thepresent disclosure.

FIG. 10b describes operations by the terminal to perform repetitivetransmission on uplink HARQ process shown in FIG. 9.

In step 1011, the terminal receives information on LTE cell from thebase station and receives at least one of HARQ timing information andrepetitive transmission-related configuration information configured bythe base station.

The information on LTE cell may be UL-DL configuration information andspecial subframe configuration information. The information on LTE cellmay be received from the base station through system information (e.g.,SIB information) or higher layer information (i.e., higher layersignaling). The repetitive transmission-related information, e.g.,repetitive transmission start subframe, repetitive transmission count,information on frequency resources for transmitting repetitivetransmission channel, or information on groups of (downlink or uplink)subframes where repetitive transmission may be conducted, may betransmitted to the terminal via system information, higher layerinformation, or L1 signal. The HARQ timing information may beinformation indicating p1 and p2 as shown in FIG. 9, and thisinformation may be transmitted through system information (e.g., SIBinformation) or higher layer information (i.e., higher layer signaling).Alternatively, the HARQ timing information may be fixed to a particularfollowing the standard, and in such case, this information might not betransmitted to the terminal. It is assumed that the terminal (e.g., alow-cost terminal) is always set in coverage enhancing mode, and in caseit is set in the coverage enhancing mode, it may communicate datathrough reception transmission/reception. The coverage enhancing mode ofthe terminal may be set by a higher layer signaling from the basestation, and the terminal always operating in the coverage enhancingmode may signal to the base station that it is always operating in thecoverage enhancing mode. Or, the terminal may set itself to operate inthe coverage enhancing mode through reception of system information or arandom access procedure or the terminal may be set to operate in thecoverage enhancing mode by the base station.

In step 1012, the terminal repeatedly receives uplink schedulinginformation based on the received repetitive transmission-relatedinformation in all the downlink subframes or downlink subframes in agroup of downlink subframes where the configured repetitive transmissionmay be performed by a higher layer signal.

In step 1013, the terminal repeatedly transmits uplink data based on theconfigured repetitive transmission-related information in the closestuplink subframe coming p1 subframes after the downlink subframe wherethe repetitive reception of uplink scheduling information is complete.

In step 1014, the terminal repeatedly receives HARQ-ACKs (ePDCCH orePHICH) based on the received repetitive transmission-relatedinformation in the closest subframe within the group of downlinksubframes where the configured repetitive transmission may be performedby a higher layer signal among the subframes coming after the p2subframes or the closest downlink subframe coming p2 subframes after theuplink subframe where the repetitive transmission of uplink data iscomplete.

FIG. 11 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 11 exemplifies a static TDD-based LTE cell 1101. The base stationperforms transmission so that the repetitive transmission of uplink datascheduling information is finished in the downlink subframe having theuplink HARQ process of LTE cell defined. That is, the base station mayhave the repetitive transmission of uplink data scheduling informationended in the downlink subframe having the uplink HARQ process defined byadjusting the subframe where the repetitive transmission of uplink datascheduling information is initiated or dynamically adjusting (reducingor increasing) the number of times of repetitive transmission.Accordingly, the terminal may perform uplink HARQ repetitivetransmission according to the uplink HARQ timing of the subframes havingthe uplink HARQ process defined.

Downlink subframes and uplink subframes are configured in the cell 1101according to TDD UL-DL configuration #4. The terminal may obtain TDDUL-DL configuration for the cell from system information (e.g., SIBinformation) or higher layer information (i.e., higher layer signaling).It is assumed that the terminal (e.g., a low-cost terminal) is alwaysset in coverage enhancing mode, and in case it is set in the coverageenhancing mode, it may communicate data through receptiontransmission/reception. The coverage enhancing mode of the terminal maybe set by a higher layer signaling from the base station, and theterminal always operating in the coverage enhancing mode may signal tothe base station that it is always operating in the coverage enhancingmode. Or, the terminal may set itself to operate in the coverageenhancing mode through reception of system information or a randomaccess procedure or the terminal may be set to operate in the coverageenhancing mode by the base station.

A TDD-based downlink subframe and uplink subframe may configure oneuplink HARQ process. The subframes having such pattern as shown in FIG.11 configure one HARQ process. In FIG. 11, downlink subframes #0, #1,#4, #5, #6, and #7 of radio frame i do not configure uplink HARQprocess, and it may be seen that subframes #0, #1, #4, #5, #6, and #7have no uplink HARQ timing defined based on uplink HARQ process.Accordingly, the HARQ transmission scheme shown in FIG. 11 mayadvantageously apply to the situations where the number of downlinksubframes configuring no uplink HARQ process in the radio frame islarger as compared with other UL-DL configurations (i.e., among theUL-DL configurations, ones having relatively fewer downlink subframesconfiguring HARQ processes). For a reason, many of the subframesconfiguring a radio frame do not configure uplink HARQ process, andthus, it would take long to perform repetitive transmission only withthe subframes configuring uplink HARQ process.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal.

A group of uplink or downlink subframes may be a group of downlinksubframes for transmission of, e.g., uplink or downlink scheduling. Ifthe repetitive transmission-related information is transmitted to theterminal and configured, the terminal may attempt to detect PDCCH (orePDCCH) for uplink or downlink scheduling only in at least one downlinksubframe in the group of downlink subframes. Further, the terminal mayalso try to detect PDCCH (or ePDCCH) for uplink or downlink schedulingonly in at least one downlink subframe within the group of downlinksubframes also for the PDCCH (or ePDCCH) for scheduling retransmissiondata after repetitive transmission of uplink data by the uplinkscheduling or repetitive transmission of downlink data by downlinkscheduling.

In FIG. 11, it is assumed that a total of four times of repetitivetransmission is set. Although the instant embodiment illustrates anexample in which the uplink scheduling information, uplink data, andHARQ-ACK are set to have the same number of times of repetition, suchpieces of information may be set to be different from each other by ahigher layer signal or may be adjusted to be different dynamically by anL1 signal.

The base station transmits uplink data scheduling information to theterminal through repetitive transmission in subframe #5, subframe #6,subframe #7, and subframe #8 of radio frame k 1102 (1111, 1112, 1113,and 1114). The base station performs repetitive transmission four timesfrom subframe #5 so that the repetitive transmission of schedulinginformation is complete in subframe #8 of radio frame k 1102. subframe#8 of radio frame k 1102 is the subframe having an uplink HARQ processdefined.

Next, the terminal repeatedly transmits uplink data (PUSCH) based on theuplink HARQ timing defined in subframe #8 of radio frame k 1102, whichis the last subframe of the repetitive transmission of schedulinginformation. That is, the terminal starts the repetitive transmission ofuplink data from subframe #2 of radio frame k+1 1103 based on the uplinkHARQ process defined in subframe #8 of radio frame k 1102 (1121).Subsequently, the terminal performs repetitive transmission in subframe#3 of radio frame k+1 1103, subframe #2 of radio frame k+2 1104, andsubframe #3 of radio frame k+2 1104 as many times as the remainingrepetition count (1122, 1123, and 1124).

Next, repetitive transmission of HARQ-ACKs (ePDCCH or ePHICH) is startedfrom the subframe according to the uplink HARQ timing based on theuplink HARQ process defined in subframe #3 of radio frame k+2 1104(i.e., subframe #9 of radio frame k+2 1104). That is, the base stationstarts HARQ-ACK repetitive transmission from subframe #9 of radio framek+2 1104 (1131). The base station repeatedly transmits HARQ-ACKs insubframe #0, subframe #1, and subframe #4 of radio frame k+3 (1105) asmany times as the remaining repetition count (1132, 1133, and 1134).

Additionally, if there is repetitive transmission for uplink dataretransmission, transmission HARQ timing needs to be determined. Sinceno uplink HARQ timing is defined in subframe #4 of radio frame k+3 1105where the HARQ-ACK repetitive transmission has been complete, theterminal is assumed to perform repetitive transmission of HARQ-ACKs morethan the repetition count indicated by an L1 signal or the repetitioncount as set. The additional repetitive transmission assumed above mayhave a level value next to the number of times of repetitivetransmission (i.e., the repetition count) set by the higher layersignal. For example, if the repetition count may be set to 1, 2, 4, or 8by a higher layer signal, and the repetition count as set is 4, theterminal may assume that the repetition count is 8 while assuming thatfour(=8-4) times of repetitive transmission is additionally performed.Or, the additional repetitive transmission assumed may have a count ofrepetitive transmission up to the subframe having a next uplink HARQtiming defined. For example, the base station may repeatedly transmitHARQ-ACKs (ePDCCH or ePHICH) up to subframe #8 of radio frame k+3 1105,which is the subframe having the next uplink HARQ timing defined (1141,1142, 1143, and 1144), and the terminal may attempt to receive HARQ-ACKs(ePDCCH or ePHICH) up to subframe #8 of radio frame k+3 1105. Theadditional repetition count may have a level (or resolution) value thatcannot be set by higher layer signals. That is, the additionalrepetition count may have any other value than 1, 2, 4, or 8.Resultantly, the terminal may perform uplink data repetitivetransmission based on the uplink HARQ timing defined in subframe #8 ofradio frame k+3 1105, and the base station may repeatedly receive uplinkdata that is retransmitted based on the uplink HARQ timing.

Alternatively, when the base station performs the HARQ-ACK repetitivetransmission from subframe #9 of radio frame k+2 1104, the base stationmay perform such HARQ-ACK repetitive transmission assuming such arepetition count as to allow the repetitive transmission to be ended inthe subframe having an uplink HARQ timing defined, and the terminal mayattempt to decode the HARQ-ACKs repeated transmitted in consistence withthe operation. Here, the terminal may operate in two ways. First, theterminal may attempt decoding at a repetition count of 1, 2, 4, or 8that may be set by a higher layer signal or L1 signal while assumingthat the repetitive transmission is finished in the subframe having theuplink HARQ timing defined. In the first case, the subframecorresponding to the set repetition count may be always defined as thesubframes having the uplink HARQ timing defined. Second, the terminalmay attempt to receive the HARQ-ACK repetitive transmission under theassumption that the repetitive transmission is finished in the subframewhere the closest uplink HARQ timing is defined, which comes apredetermined number (e.g., 4) subframes after subframe #9. In thesecond case, the base station and the terminal recognize that repetitivetransmission may be performed at any other repetition count than 1, 2,4, or 8 as settable by a higher layer signal or L1 signal.

Any one or both of the determination of uplink transmission startsubframe based on the uplink data scheduling information transmissionsubframes upon initial transmission as described in connection with FIG.11 (ePDCCH-to-PUSCH HARQ timing determination) and the determination ofuplink data transmission start subframe based on uplink data schedulinginformation transmission subframes upon retransmission (retransmissionePDCCH-to-PUSCH HARQ timing determination) may apply to the base stationand the terminal.

FIG. 12 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 12 exemplifies a static TDD-based LTE cell 1101. Although anexample has been described in which the base station transmits uplinkdata scheduling information, an example where downlink data schedulinginformation is transmitted is described in connection with FIG. 12.Described is a scheme in which the base station performs repetitivetransmission on downlink data scheduling information on LTE cell, thebase station performs repetitive transmission of downlink data accordingto the data transmission timing after the repetitive transmission of thescheduling information, and the terminal repeatedly transmits HARQ-ACKsaccording to HARQ-ACK transmission timings after the repetitivetransmission of the downlink data. Specifically, the base stationperforms repetitive transmission of downlink data in the closestdownlink subframe coming a predetermined number (n1) of subframes afterthe subframe where the repetitive transmission of downlink datascheduling information has been complete.

Downlink subframes and uplink subframes are configured in the cell 1201according to TDD UL-DL configuration #2. The terminal may obtain TDDUL-DL configuration for the cell from system information (e.g., SIBinformation) or higher layer information (i.e., higher layer signaling).It is assumed that the terminal (e.g., a low-cost terminal) is alwaysset in coverage enhancing mode, and in case it is set in the coverageenhancing mode, it may communicate data through receptiontransmission/reception. The coverage enhancing mode of the terminal maybe set by a higher layer signaling from the base station, and theterminal always operating in the coverage enhancing mode may signal tothe base station that it is always operating in the coverage enhancingmode. Or, the terminal may set itself to operate in the coverageenhancing mode through reception of system information or a randomaccess procedure or the terminal may be set to operate in the coverageenhancing mode by the base station.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal.

A group of uplink or downlink subframes may be a group of downlinksubframes for transmission of, e.g., uplink or downlink scheduling. Ifthe repetitive transmission-related information is transmitted to theterminal and configured, the terminal may attempt to detect PDCCH (orePDCCH) for uplink or downlink scheduling only in at least one downlinksubframe in the group of downlink subframes. Further, the terminal mayalso try to detect PDCCH (or ePDCCH) for uplink or downlink schedulingonly in at least one downlink subframe within the group of downlinksubframes also for the PDCCH (or ePDCCH) for scheduling retransmissiondata after repetitive transmission of uplink data by the uplinkscheduling or repetitive transmission of downlink data by downlinkscheduling.

In FIG. 12, it is assumed that a total of four times of repetitivetransmission is set. Although the instant embodiment illustrates anexample in which the uplink scheduling information, uplink data, andHARQ-ACK are set to have the same number of times of repetition, suchpieces of information may be set to be different from each other by ahigher layer signal or may be adjusted to be different dynamically by anL1 signal.

The base station transmits downlink data scheduling information to theterminal through repetitive transmission in subframe #1, subframe #3,subframe #4, and subframe #5 of radio frame k 1202 (1211, 1212, 1213,and 1214). Although examples 1211, 1211, 1213, and 1214 have beendescribed in connection with FIG. 12, where downlink schedulinginformation is transmitted in continuous downlink subframes, repetitivetransmission of downlink scheduling information may also be performed inonly downlink subframes within the group of downlink subframes where theconfigured repetitive transmission may be performed by a higher signal.

In FIG. 12, the repetitive transmission of downlink data schedulinginformation has been complete in subframe #5 of radio frame k 1202, andthe base station starts the transmission of downlink data in the closestdownlink subframe coming n1 subframes after subframe #5 of radio frame k1202 (i.e., subframe #8 of radio frame k 1202) (1215). n1 may be set asone of multiple values by a higher layer signal or may be fixed to aparticular value by a standard. For example, n1 may be fixed to 3.

After the repetitive transmission (1215) of downlink data is initiatedby the base station in subframe #8 of radio frame k 1202, the basestation performs repetitive transmission of downlink data in subframe #9of radio frame k 1202 and subframe #0 and subframe #1 of radio frame k+11203 as many times as the remaining repetition count (1216, 1217, and1218).

The following two schemes are proposed for timings for performingHARQ-ACK repetitive transmission by the terminal for the downlink datatransmission.

A first scheme is to perform HARQ-ACK repetitive transmission fromsubframe #7 of radio frame k+1 1203, which is the closest uplinksubframe coming n2 subframes after subframe #1 of radio frame k+1 1203.n2 may be set as one of multiple values by a higher layer signal or maybe fixed to a particular value by a standard. For example, n2 may befixed to 4. Accordingly, the terminal may start HARQ-ACK repetitivereception from subframe #7 of radio frame k+1 1203 (1219). The terminalmay perform HARQ-ACK repetitive transmission in subframe #2 and subframe#7 of radio frame k+2 1204 and subframe #2 of radio frame k+3 1205 asmany times as the remaining repetition count (1220, 1221, and 1222).

The second scheme is that the terminal determines an uplink subframe forHARQ-ACK transmission from the subframe where downlink data repetitivetransmission is complete based on DL-reference UL/DL configuration. TheDL-reference UL/DL configuration is a TDD UL-DL configuration receivedfrom system information when no enhanced interference management andtraffic adaption (eIMTA) is configured or when the terminal does notsupport the eIMTA or may be eimta-HarqReferenceConfig-r12 defining anuplink HARQ-ACK timing for repetitive transmission of downlink datareceived from a higher signal when the eIMTA is supported andconfigured. For example, in case the terminal does not support the eIMTAor has no eIMTA configured, when the DL-reference UL/DL configuration is#2, n2 defined in subframe #1 is 6. Accordingly, HARQ-ACK repetitivetransmission may be performed from subframe #7 that is the subframecoming six subframe #s after subframe #1 (1219). The terminal mayperform HARQ-ACK repetitive transmission in subframe #2 and subframe #7of radio frame k+2 1204 and subframe #2 of radio frame k+3 1205 as manytimes as the remaining repetition count (1220, 1221, and 1222). Asanother example, in case the eIMTA is configured in the terminal andsupported, when the DL-reference UL/DL configuration is #5, n2 definedin subframe #1 is 11. Accordingly, repetitive transmission of HARQ-ACKsmay be performed from uplink subframe #2 of radio frame k+2 1204, whichis the subframe coming 11 subframes after subframe #1 of radio frame k+11203 (1220).

Further, in the embodiment shown in FIG. 12, since repetitivetransmission of the same downlink data is performed in each subframe,there is no need of HARQ-ACK multiplexing transmission through timedomain bundling in the TDD cell, and the terminal may transmit PUCCHformat 1a/1b upon transmission of HARQ-ACK. The transmission resource ofPUCCH format 1a/1b may be determined in association with the PRB orsubband index of the (E)PDCCH first transmitted or PRB or subband indexof the (E)PDCCH transmitted last. Or, the transmission resource of PUCCHformat 1a/1b may also be determined through the PRB or subband index ofall (E)PDCCHs transmitted repeatedly.

FIG. 13 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 13 exemplifies a FDD-based LTE cell 1301. FIG. 13 illustrates anexample in which in the FDD cell the base station transmits downlinkdata scheduling information. The cell 1301 is of FDD type and has adownlink frequency f1 and an uplink frequency f2. The base stationperforms repetitive transmission of downlink data scheduling informationin the downlink subframe of DL cell f1, after the repetitivetransmission of scheduling information is ended, performs downlink datarepetitive transmission according to the data transmission timing, andafter the transmission of downlink data is ended, repeatedly transmitsHARQ-ACKs in uplink subframes of UL cell f2 depending on the HARQ-ACKtransmission timing. Specifically, the base station performs downlinkdata transmission in the downlink subframe k1 subframes after thesubframe where the repetitive transmission of the scheduling informationhas been complete.

The terminal may obtain the downlink frequency f1 while performing cellsearch and may obtain the uplink frequency f2 by receiving systeminformation from the base station. It is assumed that the terminal(e.g., a low-cost terminal) is always set in coverage enhancing mode,and in case it is set in the coverage enhancing mode, it may communicatedata through reception transmission/reception. The coverage enhancingmode of the terminal may be set by a higher layer signaling from thebase station, and the terminal always operating in the coverageenhancing mode may signal to the base station that it is alwaysoperating in the coverage enhancing mode. Or, the terminal may setitself to operate in the coverage enhancing mode through reception ofsystem information or a random access procedure or the terminal may beset to operate in the coverage enhancing mode by the base station.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal.

A group of uplink or downlink subframes may be a group of downlinksubframes for transmission of, e.g., uplink or downlink scheduling. Ifthe repetitive transmission-related information is transmitted to theterminal and configured, the terminal may attempt to detect PDCCH (orePDCCH) for uplink or downlink scheduling only in at least one downlinksubframe in the group of downlink subframes. Further, the terminal mayalso try to detect PDCCH (or ePDCCH) for uplink or downlink schedulingonly in at least one downlink subframe within the group of downlinksubframes also for the PDCCH (or ePDCCH) for scheduling retransmissiondata after repetitive transmission of uplink data by the uplinkscheduling or repetitive transmission of downlink data by downlinkscheduling.

In FIG. 13, it is assumed that a total of four times of repetitivetransmission is set. Although the instant embodiment illustrates anexample in which the uplink scheduling information, uplink data, andHARQ-ACK are set to have the same number of times of repetition, suchpieces of information may be set to be different from each other by ahigher layer signal or may be adjusted to be different dynamically by anL1 signal.

The base station transmits downlink data scheduling information to theterminal through repetitive transmission in subframe #0, subframe #1,subframe #2, and subframe #3 of radio frame k 1302 (1311, 1312, 1313,and 1314). Although examples 1311, 1312, 1313, and 1314 have beendescribed herein, where downlink scheduling information is transmittedin continuous downlink subframes, repetitive transmission of downlinkscheduling information may also be performed in only downlink subframeswithin the group of downlink subframes where the configured repetitivetransmission may be performed by a higher signal.

In FIG. 13, the repetitive transmission of downlink data schedulinginformation has been complete in subframe #3 of radio frame k 1302, andthe transmission of downlink data is started in the downlink subframecoming k1 subframes after subframe #3 of radio frame k 1302 (i.e.,subframe #6 of radio frame k 1302) (1315). k1 may be set as one ofmultiple values by a higher layer signal or may be fixed to a particularvalue by a standard. For example, k1 may be fixed to 3.

After the repetitive transmission (1315) of downlink data is initiatedby the base station in subframe #6 of radio frame k 1302, the basestation performs repetitive transmission of downlink data in subframe#7, subframe #8, and subframe #9 of radio frame k 1302 as many times asthe remaining repetition count (1316, 1317, and 1318).

Next, repetitive transmission of HARQ-ACKs is started from subframe #3of radio frame k+1 1303 which is the uplink subframe coming k2 subframesafter subframe #9 of radio frame k 1302. k2 may be set as one ofmultiple values by a higher layer signal or may be fixed to a particularvalue by a standard. For example, k2 may be fixed to 4. Here, theterminal may perform HARQ-ACK repetitive transmission from subframe #3of radio frame k 1302 (1319). The terminal may perform HARQ-ACKrepetitive transmission in subframe #4, subframe #5, and subframe #6 ofradio frame k+1 1303 as many times as the remaining repetition count(1320, 1321, and 1322).

FIG. 14 is a view illustrating a method for transmitting a controlchannel according to an embodiment of the present disclosure.

FIG. 14 exemplifies a FDD-based LTE cell 1401. FIG. 14 illustrates anexample in which in the FDD cell the base station transmits uplink datascheduling information. The cell 1301 is of FDD type and has a downlinkfrequency f1 and an uplink frequency f2. Described is a scheme in whichthe base station performs repetitive transmission of uplink datascheduling information in the downlink subframe of DL cell f1, theterminal performs uplink data repetitive transmission in the uplinksubframe of UL cell f2 according to the new uplink HARQ timing, and thebase station performs HARQ transmission according to the new uplink HARQtiming. Specifically, the base station performs uplink data repetitivetransmission in the uplink subframe m1 subframes after the subframewhere the repetitive transmission of the uplink data schedulinginformation has been complete.

The terminal may obtain the downlink frequency f1 while performing cellsearch and may obtain the uplink frequency f2 by receiving systeminformation from the base station. It is assumed that the terminal(e.g., a low-cost terminal) is always set in coverage enhancing mode,and in case it is set in the coverage enhancing mode, it may communicatedata through reception transmission/reception. The coverage enhancingmode of the terminal may be set by a higher layer signaling from thebase station, and the terminal always operating in the coverageenhancing mode may signal to the base station that it is alwaysoperating in the coverage enhancing mode. Or, the terminal may setitself to operate in the coverage enhancing mode through reception ofsystem information or a random access procedure or the terminal may beset to operate in the coverage enhancing mode by the base station.

Repetitive transmission-related information on the base station and theterminal, e.g., repetitive transmission start subframe, repetitivetransmission count, information on frequency resources for transmittingrepetitive transmission channel, or information on groups of downlink oruplink subframes where repetitive transmission may be conducted, may bepreviously transmitted to the terminal or transmitted to the terminalvia a L1 (Layer 1, physical layer) signal.

A group of uplink or downlink subframes may be a group of downlinksubframes for transmission of, e.g., uplink or downlink scheduling. Ifthe repetitive transmission-related information is transmitted to theterminal and configured, the terminal may attempt to detect PDCCH (orePDCCH) for uplink or downlink scheduling only in at least one downlinksubframe in the group of downlink subframes. Further, the terminal mayalso try to detect PDCCH (or ePDCCH) for uplink or downlink schedulingonly in at least one downlink subframe within the group of downlinksubframes also for the PDCCH (or ePDCCH) for scheduling retransmissiondata after repetitive transmission of uplink data by the uplinkscheduling or repetitive transmission of downlink data by downlinkscheduling.

In FIG. 14, it is assumed that a total of four times of repetitivetransmission is set. Although the instant embodiment illustrates anexample in which the uplink scheduling information, uplink data, andHARQ-ACK are set to have the same number of times of repetition, suchpieces of information may be set to be different from each other by ahigher layer signal or may be adjusted to be different dynamically by anL1 signal.

The base station transmits uplink data scheduling information to theterminal through repetitive transmission in subframe #0, subframe #1,subframe #2, and subframe #3 of radio frame k 1402 (1411, 1412, 1413,and 1414). Although examples 1411, 1412, 1413, and 1414 have beendescribed herein, where uplink scheduling information is transmitted incontinuous downlink subframes, repetitive transmission of uplinkscheduling information may also be performed in only downlink subframeswithin the group of downlink subframes where the configured repetitivetransmission may be performed by a higher signal.

In FIG. 14, the repetitive transmission has been complete in subframe #3of radio frame k 1402, and the terminal performs the repetitivetransmission of uplink data in the uplink subframe coming ml subframesafter subframe #3 of radio frame k 1402 (i.e., subframe #7 of radioframe k 1402) (1415). m1 may be set as one of multiple values by ahigher layer signal or may be fixed to a particular value by a standard.For example, ml may be fixed to 4.

After the repetitive transmission (1415) of uplink data is initiated bythe terminal in subframe #7 of radio frame k 1402, the terminal performsrepetitive transmission of uplink data in subframe #8 and subframe #9 ofradio frame k 1402 and subframe #0 of radio frame k+1 1403 as many timesas the remaining repetition count (1416, 1417, and 1418).

Next, repetitive transmission of HARQ-ACKs (ACKs/NACKs for UL grantswhich are transmitted through ePDCCH, MPDCCH, or M-PDCCH) is startedfrom the downlink subframe (i.e., subframe #4 of radio frame k+1 1403)coming m2 subframes after subframe #0 of radio frame k+1 1403. Or,repetitive transmission of HARQ-ACKs (ePDCCH) may be performed from theclosest subframe in the group of downlink subframes where the configuredrepetitive transmission may be performed by a higher layer signal amongthe subframes coming m2 subframes after subframe #0 of radio frame k+11403. Here, the terminal will detect HARQ-ACK (ePDCCH) only in thesubframes within the subframe group. m2 may be set as one of multiplevalues by a higher layer signal or may be fixed to a particular value bya standard. For example, m2 may be fixed to 4. Accordingly, the basestation performs HARQ-ACK (ePDCCH) repetitive transmission from subframe#4 of radio frame k+1 1403 (1419). The base station performs HARQ-ACK(ePDCCH) repetitive transmission in subframe #5, subframe #6, andsubframe #7 of radio frame k+1 1403 as many times as the remainingrepetition count (1420, 1421, and 1422).

Any one or both of the determination of uplink transmission startsubframe based on the uplink data scheduling information transmissionsubframes as described in connection with FIG. 14 (ePDCCH-to-PUSCH HARQtiming determination) and the determination of HARQ-ACK transmissionstart subframe based on uplink data transmission subframes(PUSCH-to-HARQ-ACK timing determination) may apply to the base stationand the terminal.

In all of the above-described embodiments (FIGS. 5 to 14), since thesame data is repeatedly transmitted in each subframe, the ‘DL/ULdownlink assignment index (DAI)’ field and the ‘HARQ process number’field defined in the (E)PDCCH of TDD cell may be reserved, fixed to aparticular value (e.g., ‘0’), or the fields may be disregarded by theterminal regardless of what values are set thereto. Or, the (E)PDCCH maybe configured without the fields, and the terminal may decode the(E)PDCCH assuming that the payload size of the (E)PDCCH except thefields.

In all of the above-described embodiments (FIGS. 5 to 14), since thesame data may be repeatedly transmitted in each subframe, the‘redundancy version’ field defined in the (E)PDCCH may be reserved,fixed to a particular value (e.g., ‘0’), or may be disregardedregardless of what values are set thereto. Or, the (E)PDCCH may beconfigured without the field, and the terminal may decode the (E)PDCCHassuming that the payload size of the (E)PDCCH except at least the‘redundancy version’ field. During each repetitive transmission, the‘redundancy version’ may be configured by a higher layer signal or fixedby a standard, and the terminal may decode data according to theredundancy version.

In all of the above-described embodiments (FIGS. 5 to 14), the value setfor initial repetitive transmission may be reused as the ‘redundancyversion’ for each retransmission, and the terminal may decode dataaccording to the reused ‘redundancy version.’

In all of the above-described embodiments (FIGS. 5 to 14), the number oftimes of repetitive transmission upon each retransmission may be set bya higher layer signal, and in case data reception fails upon initialrepetitive transmission, a larger repetition count may be used uponrepetitive transmission through retransmission. That is, the basestation may set a repetition count that may be used upon repetitivetransmission through retransmission for the terminal by a higher layersignal. Or, in case a larger repetition count is determined by astandard to be used upon repetitive transmission through retransmission,the base station may automatically perform repetitive transmissionthrough retransmission at a larger repetition count, and the terminalmay automatically attempt to decode using a larger repetition count uponrepetitive reception through retransmission.

FIGS. 15a and 15b are views illustrating a communication networkincluding an LAA cell to which the present disclosure applies.

Considering that the number of licensed bands, such as LTE (this term isused to collectively refer to LTE-A or other advanced versions of LTE)frequency, is limited, it is being researched to provide LTE services onan unlicensed band such as 5 GHz band, and this is called licensedassisted access (LAA). In case LAA is adopted, what is considered isthat carrier aggregation (CA) for LTE-A applies so that licensed bandLTE cell is operated as a primary serving cell (Pcell), and unlicensedband LAA cell is operated as a secondary serving cell (Scell).Accordingly, like in LTE-A, feedbacks generated in the LAA cell that isan S Cell should be transmitted only from the P cell, and the FDD andTDD1 may apply to the LAA cell.

FIG. 15a illustrates an example in which an LTE cell 1502 and an LAAcell 1503 coexist in a single small-sized base station 1501 over acommunication network.

The terminal 1504 communicates data with the base station through theLTE cell 1502 and the LAA cell 1503. In this case, there is nolimitation on the duplex scheme (i.e., whether FDD or TDD) of the LTEcell 1502 or LAA cell 1503. However, uplink transmission may beperformed only through the LTE cell 1502 in case the LTE cell 1502 is aPcell.

FIG. 15b illustrates an example in which an LTE macro base station 1511for larger coverage and an LAA small-sized base station 1512 forincreasing data transmission are installed in a communication network.

There is no limitation on the duplex scheme of the LTE macro basestation 1511 or LAA small-sized base station 1512. However, uplinktransmission is performed only through the LTE base station 1511 in casethe LTE base station 1511 is a Pcell. At this time, the LTE base station1511 and the LAA base station 1512 are assumed to have an ideal backhaulnetwork. Accordingly, fast inter-base station X2 communication 1513 ispossible, and even when uplink transmission is made only to the LTE basestation 1511, the LAA base station 1512 may receive relevant controlinformation from the LTE base station 1511 in real-time via the X2communication 1513. In the systems shown in FIGS. 15A and 15B, the LTEcell and LAA cell each may have a plurality of serving cells and theytogether may support up to 32 serving cells. Accordingly, the schemesproposed according to the present disclosure may apply to both thesystem of FIG. 15a and the system of FIG. 15 b.

Meanwhile, in LTE Rel-12, up to five serving cells may be configured inthe terminal by CA. The terminal is configured by higher layerinformation to periodically transmit channel information for datascheduling for the base station.

In the embodiment of the present disclosure, the operation ofperiodically transmitting control information is called ‘periodicchannel information transmission’, and the ‘periodic channelinformation’ is transmitted through uplink control channel (physicaluplink control channel, PUCCH) of Pcell. Further, each serving cellindependently defines a periodic channel information transmissionoperation for terminals having CA configured. Types of information to betransmitted in the periodic channel information transmission operationinclude subband CQI, subband CQI and second PMI, wideband CQI and PMI(precoding matrix indicator), wideband first PMI, wideband CQI andsecond PMI, wideband CQI and first PMI and second PMI, RI (rankindicator), wideband CQI, RI and first PMI, RI and PTI (precoder typeindicator).

Among the pieces of information, information to be transmitted accordingtransmission modes by higher layer information is determined, andtransmission information is set to have a period and offset by higherlayer information.

In the periodic channel information transmission operation, in case inone subframe periodic channel information transmission times are thesame, one subframe has been designed to transmit only periodic channelinformation for one serving cell through PUCCH of Pcell. Further, alsoin one serving cell, in case the transmission times of multiple piecesof channel information are identical in one subframe, only one piece ofchannel information has been designed to be transmitted. In this case,priority is set by the type of information to be transmitted or with aserving cell index, so that among the periodic channel informationconfigured to be transmitted for multiple serving cells, only periodicchannel information for one serving cell is transmitted while theperiodic channel information for the other serving cells is discarded.

For example, in case transmission times for multiple pieces of channelinformation for one serving cell are identical, information including RI(rank indication) has a highest priority, and in case transmission timesfor channel information for multiple serving cells are identical, theone including RI or first PMI has a highest priority, and channelinformation of the serving cell including wideband CQI has a secondhighest priority. Further, in case pieces of channel information havingthe same priority are transmitted for different serving cells, thechannel information of serving cell having a lower serving cell indexhas a higher priority. Indeed, since Rel-10 assumes scenario with twoserving cell configurations, periodic channel information transmissionsfor multiple serving cells would not be highly likely to conflict witheach other, and collision may be easily avoided as the base station setsdifferent periodic channel information transmission periods or offsetsfor serving cells.

However, assuming a scenario with up to 32 serving cell configurationsas in Rel-13, it is difficult to avoid collision between periodicchannel information transmissions in multiple serving cells simply byallowing the base station to set different periodic channel informationtransmission periods or offsets for serving cells. Accordingly, theprobability that channel information transmission times are identical inone subframe is well larger than that in Rel-12 Further, if the terminaltransmits only one periodic channel information only in one serving cellwhile discarding periodic channel information for the remaining servingcells as defined in Rel-12, the Rel-13-based base station has difficultydoing optimal scheduling on the remaining serving cells, and thisnegative affects the volume of data transmitted to the terminal.

In case the base station transmits a UL grant including a non-periodicchannel information request for transmission of channel information formultiple serving cells, it needs transmit UL grant whenever periodicchannel information transmission times become identical in multipleserving cells or in one serving cell, this results in waste of PDCCHtransmission resources and resultantly reduced PDCCH resources forscheduling other terminals in the base station. Accordingly, in case upto 32 serving cell configurations are supported for CA in Rel-13, a needcomes along for a method for supporting periodic channel informationtransmission for as many serving cells as possible in one subframewithout the need of PDCCH transmission resources.

According to the present disclosure, there are provided schemes fortransmitting channel information on multiple serving cells by a terminalwithout wasting transmission resources of downlink control channels in awireless communication system supportive of carrier aggregation.

In an embodiment of the present disclosure, UCI PUSCH transmission isdescribed.

The transmission scheme proposed in this disclosure is called UCI PUSCHtransmission in order to prevent loss of lots of channel information dueto being identical in transmission time between multiple pieces ofchannel information when transmitting periodic channel informationthrough PUCCH. The UCI PUSCH transmission according to the presentdisclosure is a method by which multiple pieces of channel informationare transmitted through PUSCH.

The mode in which the terminal performs UCI PUSCH transmission may beset by a higher layer signal. According to an embodiment of the presentdisclosure, the higher layer signal is defined as UCIPUSCHmode. IfUCIPUSCHmode is 0, i.e., if UCI PUSCH transmission mode is notconfigured, the terminal transmits only one channel information throughPUCCH in one subframe when transmitting periodic channel information (itfollows the Rel-12 operation). If UCIPUSCHmode is 1, i.e., if UCI PUSCHtransmission mode is configured, UCI PUSCH transmission is configured inthe terminal so that many pieces of channel information may betransmitted through PUSCH in one subframe. The higher layer signalUCIPUSCHmode may be replaced as the transmission resource fortransmitting channel information (UCI) being configured by a higherlayer signal. That is, the UCI PUSCH operation mode for the terminal maybe configured by having the transmission resource for transmittingperiodic channel information through PUSCH configured by a higher layersignal.

The UCI PUSCH operation by the terminal after the UCI PUSCH operationmode has been set by higher layer signal is activated as follows. First,in case the transmission times of two or more different pieces ofchannel information for one serving cell in one subframe are identical,UCI PUSCH is activated instead of PUCCH transmission. Next, in case thetransmission times of two or more pieces of channel information fordifferent serving cells in one subframe are identical, UCI PUSCH isactivated instead of PUCCH transmission. At this time, the two or morepieces of channel information for different serving cells may be thesame type of channel information or different types of channelinformation.

If UCI PUSCH is activated, the terminal multiplexes channel informationfor preset at least one or more serving cells by a preset method fortransmitting through PUSCH. Here, the pieces of channel information mayinclude all of the pieces of channel information according to theperiodic transmission configuration made to be transmitted for eachserving cell. As another example, it may include pieces of channelinformation that could not be transmitted as the channel informationtransmission times are identical, together with one piece of channelinformation that may be originally transmitted. The pieces of channelinformation may be multiplexed in the sequence depending on the type ofchannel information and serving cell index. That is, the terminal maysort the pieces of channel information per serving cell index, and thesorted pieces of channel information per serving cell index may beresorted and then multiplexed depending on the type of channelinformation. Or, the terminal may sort the pieces of channel informationper type of channel information, and the sorted pieces of channelinformation per type may be resorted and multiplexed per serving cellindex.

The channel information may be multiplexed, coded and modulated with apreset coding rate and modulation scheme, and may be transmitted to thebase station through PUSCH over preset transmission resources. Thecoding rate, modulation scheme, and transmission resource, together withUCI PUSCH operation mode, may be set by higher layer signals. As anotherexample, the coding rate, modulation scheme, and the position of initialresource, i.e., initial PRB start position, may be set by a higher layersignal, and the position of resource, i.e., the start position of PRB,may be set to be different by a predefined hopping pattern whenever eachchannel information transmission time comes identical. As inputs of thehopping pattern, radio network temporary identity (RNTI), subframenumber, and position of initial resource may be used.

According to an embodiment of the present disclosure, serving cellsperforming UCI PUSCH transmission are described.

The serving cell for transmission of UCI PUSCH may be a Pcell. SincePcell is set to transmit PUCCH, when two or more periodic channelinformation transmissions conflict, UCI PUSCH instead of PUCCH may betransmitted from Pcell, and pieces of uplink control information (UCI)transmitted through PUCCH when UCI PUSCH is transmitted may betransmitted through PUSCH (rather than through PUCCH), reducing PUCCHtransmit power.

Alternatively, serving cell for UCI PUSCH transmission may be secondarycell (Scell). In this case, one Scell of multiple Scells may be chosenas the serving cell for transmission of UCI PUSCH based on the cellindex. As an example, the Scell having the lowest cell index may bechosen as the serving cell for transmission of UCI PUSCH. If UCI PUSCHis transmitted in Scell, the UCI transmission procedure by the terminalmay be simply defined. For example, when different TDD UL-DLconfigurations apply between different bands in inter-band TDD CA, sinceUCI transmission timings in Scell and Pcell differ, a new terminalprocedure should be defined to have UCIs for Scell transmitted in Pcell.However, if UCIs for Scell are transmitted in Scell, no new terminalprocedure needs to be defined.

Subsequently, described is a method for grouping serving cells andtransmitting through uplink control channel.

FIG. 16 is a view illustrating a method for transmitting channelinformation by grouping serving cells according to an embodiment of thepresent disclosure.

This method (rather than used when channel transmission times ofdifferent serving cells are identical) is a method in which servingcells are grouped to transmit the grouping information to the terminalthrough a higher layer signal, and the terminal transmits the same,together with channel information on the grouped serving cells, throughuplink control channel.

The grouping information may indicate a group ID and at least oneserving cell included in the group. The uplink control channel throughwhich control information is transmitted may be a PUSCH that is anuplink data channel to transmit a great amount of feedback, and it mayalso be transmitted from the terminal through a new uplink controlformat.

Resource information on the PUSCH channel is previously transmitted fromthe base station to the terminal through a higher layer signal (higherlayer signaling), and since the number of serving cells included in eachgroup is already determined, the transmission resource information maybe previously configured and transmitted to the terminal by a higherlayer signal, and the terminal transmits channel information on theserving cell using the resource information. Accordingly, thetransmission resource occupancy may be optimized without waste oftransmission resources. The base station may set different transmissionperiods and offsets for different serving cell groups. As an example,the base station may choose and determine one of offsets andtransmission periods of CQI transmission used in PUCCH transmission forthe transmission periods and offsets of different serving cell groups.Accordingly, when PUSCH channel is transmitted, PUSCH transmissionsincluding different groups of channel information may be avoided frombeing identical.

FIG. 16 illustrates an example in which a total of eight serving cellgroups (e.g., 1601, 1602, 1603, 1604, and 1605) are configured for theterminal. The example shows that each cell group includes a differentnumber of cells. Further, LAA cell which is unlicensed cell and LTE cellwhich is licensed cell may be bundled into one cell group, or they maybe put in different cell groups. For example, the method of transmittingchannel information through PUSCH by the cell grouping method may applywhen the number of cells exceeds five, and in case there are five orless cells, channel information is transmitted through PUCCH, and incase at least two or more channel information transmission times areidentical, one channel information may be transmitted while the othersmay be dropped.

Further, the transmission may be performed in different PUCCH formatsdepending on the amount of channel information supposed to betransmitted in one subframe. For example, in case the pieces of channelinformation supposed to be transmitted in one subframe may betransmitted in (legacy) PUCCH format 2, the terminal may transmit thechannel information in PUCCH format 2, and in case the pieces of channelinformation supposed to be transmitted in one subframe are for multipleserving cells, the terminal may use a new PUCCH format or may performthe transmission through the PUSCH channel.

In case the pieces of channel information supposed to be transmitted bythe terminal in one subframe exceeds the payload size in which the newPUCCH format may send out or the payload size that may be included inthe PUSCH PRB upon transmission through the PUSCH channel, the terminalmay drop the pieces of channel information regarding a particular cellgroup while transmitting only the pieces of channel informationregarding the remaining cell groups. The selection of the cell group tobe dropped may be performed based on the cell group index. As anexample; there may be selected k cell groups (k is equal or largerthan 1) having lower indexes including the cell group having the lowestcell group index among the cell groups where channel information shouldbe transmitted or k cell groups having higher indexes including the cellgroup having the highest cell group index. k may be transmitted to theterminal through a higher layer signal, determined by an equation ortable, or may be previously determined as a constant. For example, whenthere is a group of serving cells whose cell group indexes are 1, 2, and3, if the payload size in which the new PUCCH format may be sent out mayinclude two cell groups, and a higher cell group index is rendered to bedropped, the pieces of channel information on the serving cells withcell group indexes 1 and 2 may be transmitted in the new PUCCH format(or through PUSCH), and the pieces of channel information on the servingcells with cell group index 3 may be dropped.

If the payload size in which transmission may be performed in the newPUCCH format (or through PUSCH) may include channel information on someserving cells of the cell group to be dropped, the channel informationon some serving cells of the cell group to be dropped may beadditionally transmitted. The selection of some serving cells may beperformed depending on the importance of channel information (e.g.,RI>wideband CQI>subband CQI), and if the pieces of channel informationhave the same importance, the selection may be performed depending onserving cell indexes (e.g., a lower index indicates a higherimportance). Channel information on serving cells that cannot betransmitted is dropped.

FIG. 17 is a view illustrating a method for communicating periodicchannel information by a base station and a terminal according to anembodiment of the present disclosure.

Described with reference to FIG. 17 is a method for setting atransmission period and offset for periodic channel informationtransmission of each serving cell according to an embodiment of thepresent disclosure. The base station may have the same effect as thatobtained by grouping serving cells in the embodiment described inconnection with FIG. 16 by setting a transmission period and offset forperiodic channel information transmission of a serving cell.

This embodiment is a method of making the channel informationtransmission times of different serving cells consistent with oneanother, so that when the pieces of channel information of the servingcells collide with each other in one subframe, the terminal alsotransmits the pieces of channel information of the serving cells throughuplink control channel.

In the method according to this embodiment, the operations exemplifiedin FIG. 17 may be selectively included, and this embodiment need not bepracticed in such a way that all of the operations are included.

The base station 1700 may allocate resources for transmission ofperiodic channel information of each serving cell (1720). At this time,the base station 1700 may make the channel information transmissiontimes of some serving cells consistent with one another.

Although the base station makes a configuration so that channelinformation transmission periods and offsets of different serving cellsare the same, the base station may transmit at least one higher layersignal to the terminal to prevent the terminal to transmit only channelinformation of one cell while dropping the others (1722 and 1724). Thehigher layer signal is a signal instructing the terminal to togethermultiplex and transmit all pieces of channel information even when thebase station makes a configuration so that channel informationtransmission periods and offsets of different serving cells are thesame. The higher layer signal transmitted from the base station may beeither or both of a configuration of uplink control format allowing agreat amount of feedback to be transmitted through uplink controlchannel (including resource configuration, channel informationtransmission period, and offset information for transmission of uplinkcontrol format) and a configuration of uplink control channel having anuplink data channel structure (including resource configuration, channelinformation transmission period, and offset information for transmissionof uplink control channel), or it may be a particular signal through ahigher layer signal.

The terminal 1710 having received the higher layer signal may select atleast one serving cell among multiple serving cells and generateperiodic channel information of the selected serving cell (1726).

The terminal 1710 may transmit the control information (UCI) includingthe generated periodic channel information on uplink through theresource indicated by the higher layer signal (1728).

According to the present disclosure, the higher layer signal forconfiguration of uplink control channel having the uplink data channelstructure is referred to as CQI-ReportPeriodicForNewPUCCHFormat 1724,and the higher layer signal for configuration of uplink control formatis referred to as CQI-ReportPeriodic 1722.CQI-ReportPeriodicForNewPUCCHFormat 1724 may be configured in additionto the higher layer signal (CQI-ReportPeriodic 1722 including theresource configuration for PUCCH format 2 transmission) for PUCCH format2, which is an uplink control format allowing the terminal to transmitthe channel information of only one cell.

In case CQI-ReportPeriodicForNewPUCCHFormat 1724 and CQI-ReportPeriodic1722 are simultaneously configured (or on and activated at the sametime), the terminal 1710 may determine whether the pieces of channelinformation of multiple cells should be simultaneously transmitted inone subframe. In case the pieces of channel information of multiplecells are not required to be simultaneously transmitted and rather thechannel information of only one cell should be transmitted, the terminal1710 transmits the periodic channel information of the single cellaccording to the transmission resource of PUCCH format 2 configured inCQI-ReportPeriodic 1722, and in case the pieces of channel informationof the multiple cells should be simultaneously transmitted, the terminal1710 may multiplex and transmit the pieces of channel information of themultiple cells according to the transmission resource of the ‘new PUCCHformat’ configured in CQI-ReportPeriodicForNewPUCCHFormat 1724.

Further, in case only CQI-ReportPeriodicForNewPUCCHFormat 1724 isconfigured (or on and activated), and CQI-ReportPeriodic 1722 is not (oroff and deactivated), the terminal 1710 may always transmit pieces ofchannel information according to the transmission resource of the newPUCCH format configured in CQI-ReportPeriodicForNewPUCCHFormat 1724regardless of whether the pieces of channel information of the multiplecells should be simultaneously transmitted in one subframe or thechannel information of only one cell should be transmitted.

Further, in case CQI-ReportPeriodicForNewPUCCHFormat 1724 is notconfigured (or set to be off and deactivated), and CQI-ReportPeriodic1722 is configured (or on and activated), if the pieces of channelinformation of multiple cells should be simultaneously transmitted inone subframe, the terminal 1710 may select and transmit the channelinformation of a cell with the highest priority according to thetransmission resource of PUCCH format 2 configured in CQI-ReportPeriodic1722. In case the pieces of channel information of multiple cells arenot required to be simultaneously transmitted and the channelinformation of only one cell should be transmitted, the terminal 1710may transmit the channel information of the single cell according to thetransmission resource of PUCCH format 2 configured in CQI-ReportPeriodic1722.

The base station 1700 may make a setting using the above-exemplifiedhigher layer signal 1724 or 1722 so that the periods and offsets oftransmission of periodic pieces of channel information of differentserving cells which should together receive pieces of channelinformation in one subframe are the same (1720). The base station 1700allows the periodic channel information transmission times (i.e.,periods and offsets) of the serving cells to be consistent, allowing forsuch an effect as if the base station 1700 intentionally grouped theserving cells that desire to simultaneously receive the pieces ofchannel information. The uplink control channel through which controlinformation is transmitted may be a PUSCH that is an uplink data channelto transmit a great amount of feedback, and it may also be transmittedthrough a new uplink control format defined by the higher layer signal.

The resource information of PUSCH channel may be previously transmittedfrom the base station 1700 to the terminal 1710 via the higher layersignal 1724 or 1722. Since the number of serving cells whose periodicchannel information transmission times have been intentionally renderedto be identical is previously determined by the base station 1700, it ispossible to previously configure resource information of PUSCH channeland to transmit the resource information to the terminal 1710 via thehigher layer signal 1724 or 1722. Accordingly, the terminal 1710 maytransmit periodic channel information of the serving cells using theresource information. Accordingly, the base station 1700 may optimizethe transmission resource occupancy without waste of transmissionresources.

As an example, the base station 1700 may make a setting so that thePcell 1611, the Scell1 1612, the Scell3 1613, and the Scell4 1614 whichare intended to be together received in one subframe as shown in FIG. 16have the same period and offset of the periodic channel informationtransmission. Here, if the periodic channel information pieces of theserving cells are set to have the same transmission period and offset,the terminal 1710 does not drop depending on the priority of theperiodic channel information pieces even when the periodic channelinformation pieces have the same transmission time, and may use acontrol channel format or PUSCH by which a great amount of controlinformation may be transmitted to transmit together the periodic channelinformation pieces in one subframe.

In case the pieces of channel information supposed to be transmitted bythe terminal 1710 in one subframe exceeds the payload size in which thenew PUCCH format may send out or the payload size that may be includedin the PUSCH PRB upon transmission through the PUSCH channel, theterminal 1710 may select a particular serving cell and may transmit thechannel information of only the selected serving cell. The selection ofthe serving cell whose periodic channel information is to be transmittedby the terminal 1710 may be performed depending on the importance ofchannel information (e.g., RI>wideband CQI>subband CQI), andaccordingly, if the pieces of channel information have the sameimportance, the selection may be performed depending on serving cellindexes (e.g., a lower index indicates a higher importance). Theterminal 1710 may drop the channel information pieces of the servingcells which cannot be transmitted, rather than transmitting.

Now, the present disclosure proposes a specific method for definingtransmission/reception operations by a low-cost terminal with a limitedbandwidth regarding the bandwidth maximally processable within the wholechannel bandwidth or system transmission bandwidth and operating normalLTE terminal and low-cost terminal in the same system.

Hereinafter, the frequency region defined by the bandwidth available bya low-cost terminal is referred to as a subband or narrowband.

FIG. 18 is a concept view illustrating an example of configuring andoperating subband where the low-cost terminal operates within the systemtransmission bandwidth according to an embodiment of the presentdisclosure.

FIG. 18 illustrates a scheme of previously configuring and operating asubband where a low-cost terminal operates in the system transmissionbandwidth.

The size 1804 of subband where the low-cost terminal operates cannot belarger than the system transmission bandwidth 1802, and is generallyassumed as the minimum transmission bandwidth supported by the LTEsystem, i.e., 1.4 MHz (six consecutive PRBs). The subband is relativelya narrow band, and thus, the number of low-cost terminals supported withone subband may be limited. If the number of low-cost terminals to besupported by the system increases, a number of low-cost terminals may besimultaneously served by configuring/operating a plurality of subbands.FIG. 18 illustrates an example in which three subbands, i.e., subband A1810, subband B 1812, and subband C 1814 are configured in the systemtransmission bandwidth.

The low-cost terminal performs data or control signal communicationoperation through one subband at some moment. Since control channels fornormal terminals are broadband-transmitted over the system transmissionbandwidth in the control channel region 1808 of each subframe, thelow-cost terminal cannot receive the control channels for normalterminals. Here, the normal terminal is a terminal with its usedtransmission bandwidth not limited to the subband region and may referto a normal LTE terminal. Control channels and data channels forlow-cost terminal may be transmitted, mapped to the subband regionexcept the control channel region 1808. Here, the control channel anddata channel for low-cost terminal may be transmitted in the same ordifferent subframes. In case the control channel and data channel forlow-cost terminal are transmitted in different subframes, a relativetime relation may be previously defined as a fixed value or may be knownto the terminal through signaling by the base station.

Control channels for normal LTE terminal are spread over the systemtransmission bandwidth in the control channel region 1808, mapped, andtransmitted, and data channels and EPDCCH for normal LTE terminal may bemapped and transmitted according to the scheduling operation by the basestation in the remaining region except the subband where the low-costterminal operates and the control channel region 1808. However, althougha subband is assigned for low-cost terminal, in case control channel ordata channel for low-cost terminal is not transmitted at some moment,the base station may use the subband as data channel for normal LTEterminal in order to efficiently utilize radio resources.

Subband control information such as the number or position of subbandsmay be previously configured and operated. The subband controlinformation may be configured independently for downlink and uplink.Although FIG. 18 primarily illustrates for downlink, it would not harmthe representation of overall concept for uplink. However, uplink doesnot include a separate control channel region like the control region1808. The base station gives the subband control information to thelow-cost terminal through signaling. The subband control information maybe included in MIB (master information block) or SIB (system informationblock) for low-cost terminal or radio resource control (RRC) signalingfor low-cost terminal. The signaling may be commonly known to aplurality of low-cost terminals. Accordingly, the base station needinform each low-cost terminal of the subband the terminal shouldspecifically operate among the known subbands through individualadditional signaling to each low-cost terminal. For example, low-costterminal A may be set to operate on subband A 1810, low-cost terminal Bon subband B 1812, and low-cost terminal C on subband C 1814.Accordingly, each low-cost terminal may perform transmission/receptionoperation only in designated subband.

While the low-cost terminal proceeds with initial access, the terminalmay receive primary synchronization signal (PSS)/secondarysynchronization signal (SSS) and physical broadcast channel (PBCH) thatare transmitted, mapped with a middle 1.4 MHz band (e.g., the bandcorresponding to subband B 1812 in FIG. 18) in the system bandwidth. Thelow-cost terminal may detect the PSS/SSS to obtain time-frequency syncand cell ID and obtain necessary system information, MIB, through PBCHdecoding. After the initial access is complete, the low-cost terminalswitches frequency to the subband designated to the terminal andperforms transmission/reception operation.

After the initial access is complete, the low-cost terminal may alsoperform time-frequency syncing, or to obtain MIB, it may perform PSS/SSSdetection and PBCH decoding. For example, low-cost terminal A operatingon subband A 1810, in order to obtain additional time-frequency sync orMIB after initial access, may stop operating on subband A 1810 andperform PSS/SSS detection and PBCH decoding on the middle 1.4 MHz band.Low-cost terminal A, after obtaining time-frequency sync or PBCHdecoding, may resume operation on subband A 1810.

FIG. 18 illustrates an example in which the subband configuration foreach low-cost terminal is maintained for a relatively long time. Forexample, subband configuration for low-cost terminal B remains atsubband B 1812 without change from subframe i 1803 to subframe i+k 1806(k>0). When desiring to change the subband configuration, the basestation informs the terminal of change in subband configuration throughthe above-described MIB, SIB, RRC signaling or individual signaling toeach low-cost terminal.

Although the low-cost terminal communicates data and control signalswithin a relatively small subband relative to the system transmissionbandwidth, it may obtain system transmission bandwidth information andinformation on the number of CRS antenna ports for exact RE mapping oftransmitted/received signals. CRS (cell-specific reference signal) isthe reference signal (RS) that the base station transmits to theterminal to allow the terminal to reference in measuring downlinkchannel status or the base station transmits to the terminal to supportoperations by the terminal, such as channel estimation, upontransmission of downlink signals, and downlink data channel and controlchannel are mapped to other REs except the RE (resource element) wherethe CRS is mapped. The mapping pattern of CRS is determined depending onthe number of transmit antennas of the base station and is defined as alogical antenna port. The low-cost terminal may be aware of the systemtransmission bandwidth information and the information on the number ofCRS antenna ports through PBCH decoding.

Generally, in the LTE system, DCI per terminal has the same size if inthe same DCI format. However, even if in the same DCI format, the sizeof DCI for low-cost terminal may be different from the size of DCI fornormal terminal. That is, DCI for low-cost terminal may be configuredcompact to fit the size of subband where low-cost terminal operates.Accordingly, in case DCI for normal terminal and DCI for low-costterminal are mapped to time-frequency resource of the same size, arelatively lower coding rate applies to the DCI for low-cost terminal(that is, error correction by channel coding is strongly reinforced),and thus, DCI for low-cost terminal may enjoy relatively more benefit inreception capability. Thus, the low-cost terminal assumes the DCI sizedetermined depending on the size of subband, not the system transmissionbandwidth, when performing DCI decoding. By contrast, the normalterminal assumes the DCI size determined depending on the systemtransmission bandwidth.

FIG. 19 is a concept view illustrating an example in which DCI size isvaried depending on the type of terminal according to an embodiment ofthe present disclosure.

The DCI size may be determined to be different depending on the type ofterminal (i.e., low-cost terminal or normal terminal). For normalterminal, DCI size 1906 is determined by DCI format 1902 or transmissionbandwidth information 1904, and for low-cost terminal, DCI size 1910 isdetermined by DCI format 1902 or subband size 1908. The size 1908 ofsubband where the low-cost terminal operates is operated to be smallerthan the system bandwidth 1904. Resultantly, even with the same DCIformat, the DCI size 1910 of low-cost terminal is smaller than the DCIsize 1906 of normal terminal.

FIG. 20 illustrates an example of a scheduling procedure by a basestation when a normal LTE terminal and a low-cost terminal co-exist inthe same system according to an embodiment of the present disclosure.

The procedure of base station described in connection with FIG. 18 isdescribed in connection with FIG. 20.

In step 2000, the base station configures a subband where the low-costterminal operates within the system transmission bandwidth and informsthe low-cost terminal of that. The base station may configure andoperate a plurality of subbands, and may notify the low-cost terminal ofsubband control information such as the number and position of subbandsthrough higher layer signaling, such as MIB, SIB, or RRC signaling.Further, the base station may inform the low-cost terminal of thesubband where each low-cost terminal operates through individualadditional signaling.

In step 2002, when determining the scheduling for the terminal, the basestation may determine whether the scheduling is for low-cost terminal ornormal LTE terminal.

If the scheduling is for low-cost terminal, the base station configuresDCI for low-cost terminal by referring to DCI format or subband size instep 2004. In step 2006, the base station transmits the configured DCIfor low-cost terminal to the low-cost terminal through downlink controlchannel. The downlink control channel for the low-cost terminal may betransmitted, mapped to the time-frequency resource except the controlchannel region for normal LTE terminal within the subband where thelow-cost terminal operates. The base station may configure and transmitdownlink data for the low-cost terminal depending on the schedulinginformation indicated by the DCI.

If the scheduling is for normal LTE terminal, the base stationconfigures DCI for normal LTE terminal by referring to DCI format orsystem transmission bandwidth in step 2008. Further in step 2010, thebase station transmits the configured DCI to the normal LTE terminalthrough PDCCH or EPDCCH which is a downlink control channel for normalLTE terminal. The base station may configure and transmit downlink datafor the normal LTE terminal depending on the scheduling informationindicated by the DCI. PDCCH may be spread over the overall systemtransmission bandwidth 1802 during the control channel transmissionperiod 1808 shown in FIG. 18 and may be mapped not overlapping for eachterminal and may then be transmitted.

FIG. 21 is a view illustrating a procedure of obtaining DCI by alow-cost terminal operating according to an embodiment of the presentdisclosure.

The procedure of the terminal exemplified in FIG. 18 is described inconnection with FIG. 21.

In step 2100, the low-cost terminal obtains subband configurationinformation on the subband where the low-cost terminal operates from thebase station and identifies the subband through which it performstransmission/reception operation with the base station.

In step 2102, the low-cost terminal attempts to obtain DCI through blinddecoding on the downlink control channel for low-cost terminal withinthe subband obtained in step 2100.

If the low-cost terminal succeeds in the blind decoding, the low-costterminal obtains detailed control information configuring the DCI instep 2104. If the obtained control information is downlink schedulinginformation, the low-cost terminal may receive downlink data channel forlow-cost terminal by the scheduling information indicated by the DCI. Ifthe obtained control information is uplink scheduling information, thelow-cost terminal may transmit uplink data channel for low-cost terminalby the scheduling information indicated by the DCI.

If the low-cost terminal fails in the blind decoding, it may performoperation 2102 at the next time of blind decoding.

FIG. 22 is a concept view illustrating an example of operating withoutexplicitly configuring a subband where a low-cost terminal operates in asystem transmission bandwidth according to an embodiment of the presentdisclosure.

Referring to FIG. 22, a method of operating a low-cost terminal with alimited maximum processable bandwidth within the system transmissionbandwidth without explicitly configuring a subband where the low-costterminal operates is exemplified.

The low-cost terminal performs data or control signal communicationoperation within a maximally processable bandwidth at some moment. Thesize of the maximally processable bandwidth by the low-cost terminalcannot be larger than the system transmission bandwidth 2202, and isgenerally assumed as the minimum transmission bandwidth supported by theLTE system, i.e., 1.4 MHz (six consecutive PRBs). The base station, uponscheduling for the low-cost terminal, should not allocate RBs exceedingthe maximally processable bandwidth of the low-cost terminal. If thelow-cost terminal is allocated RBs exceeding the maximally processablebandwidth, the low-cost terminal determines that the schedulinginformation is wrong and disregards it. Since control channels fornormal terminal are broadband transmitted over the system transmissionbandwidth 2202 in the control channel region 2208 of each subframe, thelow-cost terminal cannot receive the control channels for normalterminals. Control channels and data channels for low-cost terminal maybe transmitted, mapped to the remaining region except the controlchannel region 2208. Although FIG. 22 primarily illustrates fordownlink, it would not harm the representation of overall concept foruplink. However, uplink does not include a separate control channelregion like the control channel region 2208.

In the instant embodiment, no separate subband is previously configuredfor low-cost terminal, and (in case the limitations for RB allocationare met), the freedom of resource utilization is advantageously largerthan that in the embodiment described in connection with FIG. 18.

The low-cost terminal, while proceeding with initial access, may receivethe PSS/SSS and PBCH transmitted, mapped with the middle 1.4 MHz band(e.g., the band corresponding to 2210 of FIG. 22) in the systembandwidth. The low-cost terminal may detect the PSS/SSS to obtaintime-frequency sync and cell ID and obtain necessary system information,MIB, through PBCH decoding. After the initial access is complete, thelow-cost terminal may also perform time-frequency syncing, or to obtainMIB, it may perform PSS/SSS detection and PBCH decoding.

As described in connection with the embodiment of FIG. 18, although thelow-cost terminal communicates data and control signals within arelatively small bandwidth relative to the system transmissionbandwidth, it may obtain system transmission bandwidth information andinformation on the number of CRS antenna ports for exact RE mapping oftransmitted/received signals.

Unlike in FIG. 18, DCI size for low-cost terminal and DCI size fornormal terminal if they are in the same DCI format are kept the same inFIG. 22. That is, the base station applies the consistent DCIconfiguration method regardless of the type of terminal (that is,regardless of whether the terminal is normal terminal or low-costterminal), leading to minimized changes to the implementation of legacybase station and reduced complexity of base station implementation. Thelow-cost terminal assumes DCI size determined system transmissionbandwidth, but not the maximum processable bandwidth of low-costterminal when performing DCI decoding.

The resource information in the frequency domain which is mapped withdownlink data or uplink data of the low-cost terminal may be providedfrom the base station to the low-cost terminal through ‘resource blockassignment’ information 2216 configuring the DCI.

Referring to FIG. 22, the base station maps and transmits the DCI forthe low-cost terminal in the DCI region 2210 of subframe i 2204 and mapsand transmits the downlink data for the low-cost terminal in the PDSCHregion 2212 of subframe i+k 2206 (k>0). The frequency band size of theDCI region 2210 and the PDSCH region 2212 cannot exceed the maximumprocessable bandwidth of the low-cost terminal.

The position of the PDSCH region 2212 which is mapped to the DCI region2210 and transmitted may be indicated by ‘resource block assignment’information 2216 transmitted through the DCI region 2210. Theinformation on the DCI region 2210 which is in the frequency domainwhere the DCI is mapped and transmitted may be previously known to thelow-cost terminal by the base station. k is determined considering thetime taken for the low-cost terminal to change frequencies, and it maybe a fixed value or may be known to the terminal by the base stationthrough separate signaling. In case k=0, that is, in case the DCI anddownlink data (PDSCH) are mapped to the same subframe and transmitted,the bandwidth sum of the DCI region 2210 and the PDSCH region 2212cannot exceed the maximum processable bandwidth of the low-costterminal.

FIG. 23 is a concept view illustrating a method for determining a DCIsize according to an embodiment of the present disclosure.

Based on the embodiment exemplified in FIG. 22, in FIG. 23, for bothnormal terminal and low-cost terminal, DCI size 2306 is determined byDCI format 2302 and transmission bandwidth 2304. Resultantly, if in thesame DCI format, DCI size for low-cost terminal and DCI size for normalterminal are the same.

FIG. 24 illustrates an example of a scheduling procedure by a basestation when a normal LTE terminal and a low-cost terminal co-exist inthe same system according to an embodiment of the present disclosure.

The procedure of base station described as an example in connection withFIG. 22 is described in connection with FIG. 24.

In step 2400, the base station configures a subband where the DCI of thelow-cost terminal is mapped and transmitted in the system transmissionbandwidth of the base station and informs the low-cost terminal of thesubband. The subband control information such as the position of theconfigured may be known to the low-cost terminal through higher layersignaling, such as MIB, SIB, or RRC signaling. Further, the base stationmay individually provide the subband control information to the low-costterminal through additional signaling.

In step 2402, when determining the scheduling for the terminal, the basestation may determine whether the scheduling to be determined is forlow-cost terminal or normal LTE terminal.

If the scheduling is for low-cost terminal, the base station configuresDCI for low-cost terminal by referring to DCI format or transmissionbandwidth in step 2404. In step 2406, the base station may map theconfigured DCI of the low-cost terminal to the time-frequency resourcesexcept the control channel region for the normal LTE terminal in thesubband configured in step 2400 and transmit to the low-cost terminal.The base station may configure downlink data (PDSCH) for the low-costterminal according to the scheduling information (i.e., the resourceblock allocation information) informed by the DCI and transmit the same.

If the scheduling is for normal LTE terminal, the base stationconfigures DCI for the normal LTE terminal by referring to DCI format ortransmission bandwidth in step 2408. In step 2410, the base station maytransmit the configured DCI to the normal LTE terminal through PDCCH orEPDCCH which is a downlink control channel for normal LTE terminal. Thebase station may configure and transmit downlink data for the normal LTEterminal depending on the scheduling information known by the DCI. ThePDCCH may be spread over the overall system transmission bandwidth 2202during the control channel region 2208 shown in FIG. 22 and may bemapped without overlapping for each terminal and may then betransmitted.

FIG. 25 is a view illustrating a procedure of obtaining DCI by alow-cost terminal operating according to an embodiment of the presentdisclosure.

The procedure of the terminal exemplified in FIG. 22 is described inconnection with FIG. 25.

In step 2500, the low-cost terminal obtains subband configurationinformation on the subband which is mapped with the DCI for low-costterminal and transmitted from the base station and identifies thesubband through which it should receive the DCI from the base station.

In step 2502, the low-cost terminal attempts to obtain DCI through blinddecoding on the downlink control channel for low-cost terminal withinthe subband obtained in step 2500.

If the low-cost terminal succeeds in the blind decoding, the low-costterminal obtains detailed control information configuring the DCI instep 2504. If the obtained control information is downlink schedulinginformation, the low-cost terminal may receive downlink data channel forlow-cost terminal by the scheduling information indicated by the DCI. Ifthe obtained control information is uplink scheduling information, thelow-cost terminal may transmit uplink data channel for low-cost terminalby the scheduling information indicated by the DCI.

If the low-cost terminal fails in the blind decoding, it may performoperation 2502 at the next time of blind decoding.

FIG. 26 is a concept view illustrating an example of previouslyconfiguring and dynamically varying a subband where a low-cost terminaloperates in a system transmission bandwidth according to an embodimentof the present disclosure.

Described with reference to FIG. 26 is an exemplary method forpreviously configuring and operating subbands where the low-costterminal operates in the system transmission bandwidth while dynamicallychanging the subbands where the low-cost terminal operates.

The size of subband where the low-cost terminal operates cannot belarger than the system transmission bandwidth 2602, and is generallyassumed as the minimum transmission bandwidth supported by the LTEsystem, i.e., 1.4 MHz (six consecutive PRBs). The base station maysimultaneously serve a number of low-cost terminals byconfiguring/operating a plurality of subbands. FIG. 26 illustrates anexample in which three subbands A, B, and C 1010, 1012, and 1014 areconfigured in the system transmission bandwidth 2602. The low-costterminal may perform data or control signal communication operationthrough one subband of the subbands at some moment.

In this embodiment, the base station may designate one of the subbands,maps it with DCI for low-cost terminal and transmits, and dynamicallyindicate the subband mapped with the data for low-cost terminal byincluding a subband indicator 2616 in the DCI. The ‘subband indicator’may be included in, e.g., the resource block assignment informationincluded in the DCI. The subband mapped with the DCI may be previouslyknown to the low-cost terminal by the base station, leading to reducedcomplexity of DCI decoding of low-cost terminal. The ‘subband indicator’2616 is information indicating the subband where the data of thelow-cost terminal is mapped and transmitted among the subbandsconfigured for use by the low-cost terminal. The subband indicator mayalso be called a ‘subband index,’ narrowband indicator,' or ‘narrowbandindex.’ The ‘subband indicator’ 2616 may also be configured in variousmethods as follows.

Method 1. adding to existing DCI as additional control information.

Method 2. switching some control information of existing DCI into‘subband indicator.’ For example, the carrier indicator field (CIF)defined for carrier aggregation (CA) may be switched and used as asubband indicator for low-cost terminal. (this is why the CA does notapply to low-cost terminals.)

Method 3. combining ‘subband indicators’ for several terminals toconfigure group control information. In this case, unlike in methods 1and 2, DCI for scheduling is required separately from the ‘subbandindicator.’

The information on the frequency domain 2612 where the ‘subbandindicator’ is mapped and transmitted is previously designated and knownto the low-cost terminal by the base station. Referring to FIG. 26, thebase station maps and transmits the ‘subframe indicator’ for thelow-cost terminal in subframe B 2612 of subframe i 2604 and maps andtransmits the downlink data for the low-cost terminal in subband A 2610of subframe i+k 2606 (k>0). k is determined considering the time takenfor the low-cost terminal to change frequencies, and it may be a fixedvalue or may be known to the terminal by the base station throughseparate signaling. In case k=0, that is, in case the ‘subbandindicator’ and downlink data are mapped and transmitted in the samesubframe, the subband where the subband indicator is delivered is thesame as the subband where the downlink data is delivered. Aftercompleting the reception of downlink data, the low-cost terminal maytake the following approaches.

Method A. The low-cost terminal goes back to the subband where the‘subband indicator’ is mapped and transmitted (i.e., changesfrequencies) to attempt to detect a next ‘subband indicator.’

Method B. The low-cost terminal, without changing subbands, prepares toreceive next downlink data or transmit uplink data within the subbandindicated by the ‘subband indicator.’

Regardless of method A or B, the low-cost terminal may obtaintime-frequency sync or change frequency into the center frequency of thesystem transmission bandwidth to obtain MIB to detect PSS/SSS and decodePBCH.

Although the low-cost terminal communicates data and control signalswithin a relatively small bandwidth relative to the system transmissionbandwidth, it may obtain system transmission bandwidth information andinformation on the number of CRS antenna ports for exact RE mapping oftransmitted/received signals.

The scheduling procedure of the base station according to FIG. 26 may bedescribed with reference to FIG. 20. However, according to theembodiment shown in FIG. 26, upon configuring DCI for low-cost terminalin step 2004 of FIG. 20, an additional subband indicator may beconfigured by method 1 or method 2 or separate group control informationobtained by combining subband indicators for several terminals may beconfigured by method 3.

The procedure of obtaining the DCI by the low-cost terminal according toFIG. 26 may be described with reference to FIG. 21. However, accordingto the embodiment shown in FIG. 26, in step 2102 or previous steps ofFIG. 21, the low-cost terminal may additionally perform the procedure ofreceiving the ‘subband indicator.’

FIG. 27 is a concept view illustrating an example of a method forindicating a subband in an FDD system according to an embodiment of thepresent disclosure.

In the frequency division duplex (FDD) system where uplink and downlinkare separately operated in the frequency domain, the interval in centerfrequency between uplink frequency and downlink frequency (TX-RX carriercentre frequency separation) is defined for each frequency band whereLTE system operates. Described with respect to FIG. 27 is described, asan example, a scheme of utilizing the center frequency interval (subbandTx-Rx centre frequency separation) between uplink subband and downlinksubband in case the uplink subband and downlink subband of the low-costterminal are each operated within each of uplink and downlinktransmission bandwidths.

FIG. 27 illustrates the interval between uplink center frequency (ULcenter frequency) 2708 and downlink center frequency (DL centerfrequency) 2710, i.e., ‘TX-RX carrier centre frequency separation’ 2700between the uplink frequency and the downlink frequency, uplinkbandwidth (BW_(UL)) 2704, downlink bandwidth (BW_(DL)) 2706, low-costterminal's uplink subband bandwidth (BW_(UL,subband)) 2712, low-costterminal's downlink subband bandwidth (BW_(DL,subband)) 2714, intervalin center frequency between uplink subband and downlink subband(‘subband Tx-Rx centre frequency separation’) 2702.

‘TX-RX carrier centre frequency separation’ 2700 and ‘subband Tx-Rxcentre frequency separation’ 2702 may have different values. Since theuplink subband 2716 and downlink subband 2718 of the low-cost terminalmay be positioned in the uplink bandwidth 2704 and the downlinkbandwidth 2706, respectively, the interval in center frequency betweenthe uplink subband and downlink subband (subband Tx-Rx centre frequencyseparation) meets the relation determined by the following Equation 1.

‘TX-RX carrier centre frequency separation’−(BW_(UL)/2−BW_(UL,subband)/2)−(BW_(DL)/2−BW_(DL,subband)/2)≤‘subband Tx-Rx centrefrequency separation’≤‘TX-RX carrier centre frequencyseparation’+(BW_(UL)/2−BW_(UL,subband)/2)+(BW_(DL)/2−BW_(DL,subband)/2)  [Equation 1]

Accordingly, the base station may apply the following methods to informthe low-cost terminal of the position of downlink subband and uplinksubband.

Method 1. The base station informs each of the low-cost terminal of theposition of downlink subband and uplink subband through signaling.

Method 2. The base station informs each of the low-cost terminal of theposition of downlink subband and interval in center frequency betweenthe uplink subband and the downlink subband (subband Tx-Rx centrefrequency separation) through signaling. In such case, the terminal maycalculate the position of the uplink subband from the signaling value.

Method 3. The base station informs each of the low-cost terminal of theposition of uplink subband and interval in center frequency between theuplink subband and the downlink subband (‘subband Tx-Rx centre frequencyseparation’) through signaling. In such case, the terminal may calculatethe position of the downlink subband from the signaling value.

In a variation to the example shown in FIG. 27, the number of uplinksubbands and the number of downlink subbands may be set to be differentdepending on asymmetry in traffic volume between uplink and downlink.

FIG. 28 is a view illustrating an exemplary configuration of a basestation for implementing an embodiment of the present disclosure.

Here, the base station may be an LTE base station or an LAA basestation. According to the present disclosure, the base station mayinclude a controller 2801 and a transceiver 2820.

The transceiver 2820 may include a transmitter including at least one ofa PDCCH block 2805, a PDSCH block 2816, a PHICH block 2824, and amultiplexer 2815 and a receiver including at least one of a PUSCH block2830, a PUCCH block 2839, and a demultiplexer 2849.

The controller 2801 may perform repetitive transmission and DL/UL HARQtiming control according to FIGS. 2 to 14 of the present disclosure.Further, the controller 2801 may perform the cell grouping and channelinformation mapping control, resource allocation for periodic channelinformation transmission and transmission of higher layer signalsaccording to FIGS. 15 to 17 of the present disclosure. Further, thecontroller 2801 may perform the DCI transmission and subband allocationof the low-cost terminal according to FIGS. 18 to 27 of the presentdisclosure depending on the type of the terminal.

The base station may further include at least one of a scheduler 2803, aDCI composer, a storage unit, and an antenna. The scheduler may performthe control of DL/UL HARQ timing. The DCI composer may configure DCI asdescribed in connection with the above embodiments of the presentdisclosure depending on the type of terminal to be scheduled by the basestation.

Here, the repetitive transmission follows the methods described aboveaccording to the present disclosure, the DL HARQ timing means the PDSCHtransmission timing for the downlink scheduling repetitive transmissionand the PUCCH transmission timing for the PDSCH repetitive transmission,and the UL HARQ timing includes the PUSCH transmission timing for theuplink scheduling information repetitive transmission and the ULgrant/PHICH transmission timing for the PUSCH repetitive transmission.

The controller 2801 may adjust timing relations between physicalchannels for the terminal, which the controller 2801 is to schedule, byreferencing, e.g., the volume of data to be transmitted to the terminaland the amount of resources available in the system and control thescheduler 2803, the PDCCH block 2805, the PDSCH block 2816, the PHICHblock 2824, the PUSCH block 2830, and the PUCCH block 2839. The controlof the repetitive transmission and UL HARQ timing follows the methodsdescribed in connection with specific embodiments of the presentdisclosure.

The PDCCH block 2805 may configure control information under the controlof the scheduler 2803 to perform repetitive transmission as describedabove in connection with specific embodiments of the present disclosure,and the control information may be multiplexed with other signals by themultiplexer 2815.

The PDSCH block 2816 may generate data under the control of thescheduler 2803. The data, together with other signals, may bemultiplexed by the demultiplexer 2815.

The PHICH block 2824 may generate the HARQ ACK/NACK for PUSCH receivedfrom the UE under the control of the scheduler 2803 with the HARQ-ACKfor PUSCH repetitive transmission to perform repetitive transmission asdescribed above in connection with specific embodiments of the presentdisclosure. The HARQ ACK/NACK together with other signals may bemultiplexed by the multiplexer 2815.

The multiplexed signals are generated into OFDM signals that are thentransmitted to the UE.

The PUSCH block 2830 may obtain PUSCH data for signals received from theUE by repetitive transmission as described above in connection withspecific embodiments of the present disclosure. Whether there is anerror in the result of decoding the PUSCH data may be notified to thescheduler 2803 to adjust downlink HARQ ACK/NACK generation and isapplied to the controller 2801 to allow the HARQ ACK/NACK transmissiontiming to be adjusted.

The PUCCH block 2830 obtains uplink ACK/NACK or CQI from the signalreceived from the UE through the HARQ-ACK payload size and PUCCH formator signal received from the UE based on the PUCCH transmission timing asdescribed above in connection with specific embodiments of the presentdisclosure. The obtained uplink ACK/NACK or CQI is applied to thescheduler 2803 and is used to determine whether to re-transmit the PDSCHand a modulation and coding scheme (MCS). The obtained uplink ACK/NACKmay be applied to the controller 2801 to adjust the transmission timingof PDSCH.

FIG. 29 is a view illustrating an exemplary configuration of a terminalfor implementing an embodiment of the present disclosure.

According to the present disclosure, the terminal may include acontroller 2901 and a transceiver 2920.

The transceiver 2920 may include a transmitter including at least one ofa PUCCH block 2905, a PUSCH block 2916, and a multiplexer 2915 and areceiver including at least one of a PHICH block 2924, a PDSCH block2930, a PDCCH block 2939, and a demultiplexer 2949.

The controller 2901 may perform repetitive transmission according toFIGS. 2 to 14 of the present disclosure. Further, the controller 2901may control the cell grouping and channel information mapping accordingto FIGS. 15 to 17 of the present disclosure and may perform a periodicchannel information transmission operation. Further, the controller 2901may perform the operations of obtaining the DCI of the low-cost terminaland communication through a subband according to FIGS. 18 to 27 of thepresent disclosure.

The terminal may further include at least one of a storage unit and anantenna.

According to the present disclosure, the controller 2901 controllingrepetitive transmission and DL/UL HARQ timing may control the PDSCHblock 2930, PDCCH block 2939, PUCCH block 2905, and PUSCH block 2916according to repetitive transmission and UL HARQ timing. Here, therepetitive transmission follows the methods described above according tothe present disclosure, the DL HARQ timing means the PDSCH transmissiontiming for the downlink scheduling repetitive transmission and the PUCCHtransmission timing for the PDSCH repetitive transmission, and the ULHARQ timing means the PUSCH transmission timing for the uplinkscheduling information repetitive transmission and the UL grant/PHICHtransmission timing for the PUSCH repetitive transmission.

The PUCCH block 2905 configures HARQ ACK/NACK or CQI with the uplinkcontrol information (UCI) under the control of the controller 2901controlling the storing of downlink data in a soft buffer for repetitivetransmission according to an embodiment of the present disclosure, andthe HARQ ACK/NACK or CQI is multiplexed with other signals by themultiplexer 2915 and transmitted to the base station.

The PUSCH block 2916 may extract the data to transmit through repetitivetransmission according to an embodiment of the present disclosure, andthe extracted data may be multiplexed with other signals by themultiplexer 2915. The multiplexed signals may be generated into singlecarrier frequency division multiple access (SC-FDMA) signals that maythen be transmitted to the base station considering UL HARQ timing.

The PHICH block 2924 in the receiver separates, through thedemultiplexer 2949, the PHICH signal from the signals received as perrepetitive transmission and UL HARQ timing from the base stationaccording to the present disclosure and then obtains whether to HARQACK/NACK for the PUSCH.

For the repetitive transmission according to an embodiment of thepresent disclosure, the PDSCH block 2930 separates the PDSCH signalthrough the demultiplexer 2949 for the signal received from the basestation and then obtains PDSCH data, notifies the PUCCH block 2905whether there is an error in the result of decoding the data to adjustgeneration of the uplink HARQ ACK/NACK, and applies whether there is anerror in the decoding result to the controller 2901 to allow timing tobe adjusted upon transmission of the uplink HARQ ACK/NACK.

The PDCCH block 2939 may separate the PDCCH signal through thedemultiplexer 2949 and then decode the DCI format to obtain the DCI fromthe decoded signal.

It should be noted that the configuration of subframe, systemconfiguration, and examples of control methods as shown in FIGS. 2 to 29are not intended as limiting the scope of the present disclosure. Inother words, all the components or operational steps illustrated inFIGS. 2 to 29 should not be construed as essential components topractice the present disclosure, and the present disclosure may berather implemented with only some of the components without departingfrom the gist of the present disclosure.

The above-described operations may be realized by equipping a memorydevice retaining their corresponding codes in an entity, function, basestation, or any component of a terminal in a communication system. Thatis, the controller in the entity, the function, the base station, or theterminal may execute the above-described operations by reading andexecuting the program codes stored in the memory device by a processoror central processing unit (CPU).

As described herein, various components or modules in the entity,function, eNB, or UE may be operated using a hardware circuit, e.g., acomplementary metal oxide semiconductor-based logic circuit, firmware,software, and/or using a hardware circuit such as a combination ofhardware, firmware, and/or software embedded in a machine-readablemedium. As an example, various electric structures and methods may beexecuted using electric circuits such as transistors, logic gates, orASICs.

Although specific embodiments of the present disclosure have beendescribed above, various changes may be made thereto without departingfrom the scope of the present disclosure. Thus, the scope of the presentdisclosure should not be limited to the above-described embodiments, andshould rather be defined by the following claims and equivalentsthereof.

What is claimed is:
 1. A method performed by a terminal in a wireless communication system, the method comprising: receiving, from a base station, downlink control information (DCI) including a subband indicator indicating a subband among at least one subband configured for the terminal as an active subband and information indicating at least one frequency resource allocated for a physical downlink shared channel (PDSCH) within the active subband; identifying the active subband based on the subband indicator; and receiving, from the base station, the PDSCH in the active subband based on the information, wherein a size of the DCI is configured based on a size of the active subband.
 2. The method of claim 1, further comprising: receiving, from the base station, another DCI including another subband indicator indicating another subband among the at least one subband as the active subband; and receiving, from the base station, another PDSCH in the another subband based on a predetermined time delay required for active subband change in the terminal.
 3. The method of claim 2, wherein the predetermined time delay is determined based on a predetermined value that is set for the terminal.
 4. The method of claim 2, wherein further comprising: receiving, from the base station, another information associated with the predetermined time delay.
 5. A method performed by a base station in a wireless communication system, the method comprising: configuring downlink control information (DCI) including a subband indicator indicating a subband among at least one subband configured for a terminal as an active subband and information indicating at least one frequency resource allocated for physical downlink shared channel (PDSCH) within the active subband; transmitting, to the terminal, the configured DCI; and transmitting, to the terminal, the PDSCH in the active subband based on the information, wherein a size of the DCI is configured based on a size of the active subband.
 6. The method of claim 5, further comprising: transmitting, to the terminal, another DCI including another subband indicator indicating another subband among the at least one subband as the active subband; and transmitting, to the terminal, another PDSCH in the another subband based on a predetermined time delay required for active subband change in the terminal.
 7. The method of claim 6, wherein the predetermined time delay is determined based on a predetermined value that is set for the terminal.
 8. The method of claim 6, further comprising: transmitting, to the terminal, another information associated with the predetermined time delay.
 9. A terminal in a wireless communication system, the terminal comprising: a transceiver; and at least one processor configured to: receive, from a base station, downlink control information (DCI) including a subband indicator indicating a subband among at least one subband configured for the terminal as an active subband and information indicating at least one frequency resource allocated for physical downlink shared channel (PDSCH) within the active subband; identify the active subband based on the subband indicator; and receive, from the base station, the PDSCH in the active subband based on the information, wherein a size of the DCI is configured based on a size of the active subband.
 10. The terminal of claim 9, wherein the at least one processor is further configured to: receive, from the base station, another DCI including another subband indicator indicating another subband among the at least one subband as the active subband; and receive, from the base station, another PDSCH in the another subband based on a predetermined time delay required for active subband change in the terminal.
 11. The terminal of claim 10, wherein the predetermined time delay is determined based on a predetermined value that is set for the terminal.
 12. The terminal of claim 10, wherein at least one processor is further configured to: receive, from the base station, another information associated with the predetermined time delay.
 13. A base station in a wireless communication system, the base station comprising: a transceiver; and at least one processor configured to: configure downlink control information (DCI) including a subband indicator indicating a subband among at least one subband configured for a terminal as an active subband and information indicating at least one frequency resource allocated for a physical downlink shared channel (PDSCH) within the active subband; transmit, to the terminal, the configured DCI; and transmit, to the terminal, the PDSCH in the active subband based on the information, wherein a size of the DCI is configured based on the size of the active subband.
 14. The base station of claim 13, wherein the at least one processor is further configured to: transmit, to the terminal, another DCI including another subband indicator indicating another subband among the at least one subband as the active subband; and transmit, to the terminal, another PDSCH in the another subband based on a predetermined time delay required for active subband change in the terminal.
 15. The base station of claim 14, wherein the predetermined time delay is determined based on a predetermined value that is set for the terminal.
 16. The base station of claim 14, wherein the at least one processor is further configured to: transmit, to the terminal, another information associated with the predetermined time delay. 